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Glossary of Terms
Compendium of
Terms Used in Ophthalmic Surgery
A
Ablation
Ablation
is the term for the process where corneal tissue is removed
using an excimer
laser. Each pulse of the laser removes a very fine amount of
tissue - usually about 0.25 micrometers
of corneal tissue. One micrometer is one thousands of a
millimetre (i.e.0.001mm). Treatment depths vary according to
the magnitude of the refractive
error being treated. See also photoablation
below.
Ablation
profile
This is the term used to describe the
particular amount and shape of corneal tissue that the excimer
laser is guided to ablate in any individual eye being
treated to correct its refractive
error. If it is designed with Wavefront
data then it is described as a customised
ablation.
Aberrations
This term refers
to the optical errors within the optical system that is the
human eye. They are measured by a Wavefront
scanning device and are essential if patients are to receive a
Wavefront correction (see higher
order aberrations below for more information).
Aberrometer
This is the name for a device
that is used to measure the higher
order aberrations of the eye. This is essential if the
centre is to be able to deliver customised Wavefront
corrections to their patients. They are also known as Wavefront
scanning devices and the one used at the Ardfallen Eye Clinic is the Bausch & Lomb system. This uses a combination of data from the Bausch & Lomb Zywave aberrometer and the Orbscan.
Ablation zone
This describes the
circular area of cornea
where the excimer
laser ablates tissue. It may be varied according the value
of other parameters such as pupil
size and amount of tissue that is being ablated.
Accommodation
The
ability of the eye to adjust its focus so that objects that
are close to the eye can be seen well. It can be used earlier
in life to overcome lower grades of hyperopia.
This declines with age and results in the requirement for
reading glasses. In otherwise normal sighted individuals this
usually occurs around the age of 45 and this is known as
presbyopia. There are other forms of treatment for presbyopia
such as conductive
keratoplasty and prelex
(see below for more information).
Acuity
The measurement of how well
we see in terms of the sharpness of our vision. This visual acuity
can be expressed in a number of different ways the most
commonly used being in the number of lines read on a Snellen
chart. The best
corrected visual acuity (i.e. BCVA) is the measurement of
the best vision with optical
aids (i.e. either glasses or contact
lenses). Uncorrected
visual acuity (i.e. UCVA) is the measurement of the vision
without any optical
aids.
Add
This term is used in optical
prescriptions to refer to the power that is added to the
distance prescription to provide a reading correction. This
will vary according to the patient's age (i.e. how long they
have been suffering from presbyopia).
Aftercare
Ardfallen Eye Clinic has
instruction sheets for patients to make their aftercare much
easier for them. As with all our service this is directed by a
consultant.
Age
The ideal laser eye surgery
correction for a patient when they are younger is for
distance. In older patients account has to be taken for presbyopia.
This has led to the concepts of monovision
for myopes and blended
vision in hyperopes
(see below for more information).
Age Related Macular
Degeneration
This disease affects the central retina in
older individuals. It results in varying degrees of damage to
the central vision. Patients can quite effectively monitor
their own central vision at home using a simple device known
as an Amsler grid. There are two types of age related macular
degeneration which are called atrophic and neovascular ARMD.
Patients can be treated occasionally with laser to the retina.
This requires the use of fluorescein
angiography to identify whether there are treatable areas or
not. Patients are now being advised to take carotenoids as
they offer a protective effect against damage from ARMD by
both filtering damaging blue light and also by their powerful
antioxidant property neutralising free radicals which are the
products of metabolising oxygen. The most recent innovation in
treatment of ARMD is the use of anti-angiogenic agents which
are delivered in the form of an injection into the vitreous
gel.
Allergy
Allergic eye disease is
quite common. It mainly affects the conjunctiva
but the skin on the eyelids is also quite likely to develop an
allergic response. Allergic conjunctivitis usually occurs in
one of two patterns. These are seasonal allergic
conjunctivitis (abbreviated as SAC) and perennial allergic
conjunctivitis (which is abbreviated as PAC). SAC tends to
occur during the high pollen counts in the spring and summer
time whereas PAC tends to occur year round. They are often
associated with a history of allergic type problems elsewhere
in the body (such as asthma and eczema) and this is then
described as atopic disease.
Amblyopia
This
is the medical term for a lazy eye. Amblyopia can be of
varying density. If it is not too dense then the potential acuity
in an amblyopic that has a refractive
error treated may justify that treatment. The decision to
treat the other eye would have to be carefully discussed and
an informed
decision could then be made.
Anaesthetic
Topical anaesthetic drops are
used to numb the eye for the purpose of examinations and they
are also used for surgical procedures such as lasik,
lasek
and cataract
operations.
Aniseikonia
When each eye has a
different refractive
error (i.e. when there is anisometropia)
then this term is used to describe the difference in the size
of the perceived image that each eye views.
Anisometropia
This term
refers to the situation where each eye has a different refractive
error with the difference being in excess of one dioptre.
Anklyosing Spondylitis
This is an
inflammatory condition that predominantly affects younger male
patients. It results in axial arthritis which mainly targets
the spine and can result in recurrent episodes of ocular inflammation.
Anterior chamber
This is the space in the
eye between the back of the cornea
and the front of the iris.
Anterior chamber angle
This is another term
for the drainage
angle (see below).
Anterior Uveitis
This
is an inflammation
of the anterior uveal
tissue.
Anterior
segment
This term is used to refer to that portion of
the eye from the crystalline
lens forward through the iris,
anterior chamber, cornea,
tear
film and conjunctiva.
The eyelids and the lacrimal glands are then called the ocular
adnexa.
Anti-inflammatories
These are drugs
that are used to suppress inflammation
and thereby they may assist in pain relief. In ophthalmology
they may be delivered in either a topical (i.e.
drops/ointment), systemic or occasionally in an injectible
vehicle.
Antibiotics
These are drugs that
are used to treat bacterial infections. In ophthalmology they
are generally delivered topically but systemic antibiotics are
also used at times. At Ardfallen Eye Clinic we routinely use
Exocin topically to clear the conjunctival
bacterial flora prior to undertaking surgery. It is important
not to overuse antibiotics as this practice will result in the
emergence of resistant strains.
Anxiety
Patients who suffer from anxiety or
depression, particularly those on any medication, should
mention this when they are booking their appointment for
assessment for any form of ophthalmic surgery.
Aphakic
This term means that the crystalline
lens of an eye has been removed. It is the opposite of
phakic.
Aqueous humour
This is the fluid
that fills the anterior portion of the eye. It is produced by
the ciliary processes in the ciliary body. The fluid drains
out of the eye via the trabecular
meshwork before it eventually gains access to the venous
system.
Arcuate keratotomy (i.e. AK)
This is
the term for an incision that is made in the cornea
to treat astigmatism.
Arcuate keratotomies are most commonly paired at opposite ends
of the steep axis of the cornea.
Their depth and arc length are designed on the basis of
various factors.
Arcuate keratotomies
These
are partial thickness incisions that are used to treat astigmatism.
Their depth and orientation are designed on the basis
magnitude of the cylinder and the orientation its axis as well
as on the thickness of the cornea
along the arc that the incision is to be made. These
parameters are measured during examination of the eye.
Astigmatism
This is
the term used to describe the situation where the cornea
has different curvatures in different meridians. astigmatism
can be described in terms of its principal axes and its
magnitude. It can be corrected with either optical
aids (i.e. spectacles or contact
lenses with a cylinder) or with various forms of refractive
surgery. If a minus cylinder is being referred to then
astigmatism is with the rule at 180 degrees and against the
rule at 90 degrees. See also our Eye Motion education centre
for more information.
Auto-refraction
This
is the term used to describe where the refractive
error of an eye is measured with an automated device known
as an auto-refractor.
Auto-refractor
This is
an automatic measuring device that measures the refractive
error of an eye.
Axis
In describing astigmatism
this term is used to define which meridian of the cornea
is being referred to. It is described in degrees from 0-180.
It can also be used to refer to the principal path that light
rays traverse to focus on the fovea.
It is then referred to as the visual
axis.
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B
Balance
Prescription
This is an optical prescription where a lens
of the same or similar power is prescribed to balance the
weight and appearance of the lenses in a spectacle frame in a
situation where one eye does not function well (e.g. in
amblyopia).
Bandage Contact Lens (i.e.
BCL)
This is a non-optical contact lens
which is placed on the eye to promote healing of the corneal
epithelium
and to make the patient more comfortable while this process is
evolving. Patients should not interfere with them and while
there is a BCL in the eye the patient will undergo regular
review examinations.
Base curve
This term is
used to describe the radius of curvature of the central
posterior surface of a contact lens.
Bausch & Lomb (i.e. B&L)
This is the large optical company that manufacture the Technolas excimer laser system that we currently use to treat refractive errors at the Ardfallen Eye Clinic. B&L also manufacturer the instruments that we use to measure the Wavefront required to treat the patients higher order aberrations. These instruments are the Zywave which is used in combination with the Orbscan. Bausch & Lomb has gained approval from the FDA in the USA for the use of its excimer laser system in the treatment of refractive errors.
Beam size
With excimer
laser treatment the beam size is what determines the size
of the zone of corneal tissue that is ablated. This may be
adjusted and it is tailored to outsize the patient's pupil
in reduced lighting conditions (which are referred to as
scotopic viewing conditions). By doing this the possibility of
haloes after laser treatment is reduced. The pupil
size is measured using an instrument known as a
pupillometer. At Ardfallen Eye Clinic we use a Procyon
pupillometer.
Best Corrected
Visual Acuity (i.e. BCVA)
This is the visual acuity
that is achieved with the ideal optical correction with optical
aids (i.e. spectacles or contact
lenses).
Bi-focals
This is a spectacle
correction where there is a different power for correcting
vision in the distance at the top of the spectacle lens and an
increased power in the lower part of the spectacle lens for
close work (such as reading). The magnitude of the increased
power is dependent on the age of the patient wearing the
bi-focals.
Binocular
This term refers to
where the two eyes are used together. If an individual's two
eyes are correctly aligned and there is no significant anisometropia
then that individual will have good stereoacuity.
Biometry
This is where a patient's eyes are
measured with a special ultrasound to determine the axial
length of their eyes. This measurement is then combined with
corneal topography measurements in various mathematical
formulas to calculate the power required in an intra-ocular
lens that is implanted in the patient's eye after their crystalline
lens has been removed (either because there is a cataract
present or in a refractive lens
exchange operation).
Blended vision
This is a
concept that is used in treating a hyperopic patient who is
also in the presbyopic
age-group. The non-dominant eye is slightly over-corrected to
allow the patient to read smaller print while the dominant eye
is corrected for distance. The two eyes are then used together
thereby allowing the patient to have good acuity
for both near and for distance.
Blepharitis
This is an inflammation/infection
of the eyelids. It is treated with a combination of regular
eyelid hygiene and occasional courses of topical and or
systemic antibiotics. It is often associated with dry eye
disease and seborrhoea and is then referred to as "triple S
syndrome". Prior to undertaking any form of ophthalmic surgery
blepharitis
should be treated and if possible eradicated.
Bowman's membrane
This is the layer of
tissue in the cornea
that lies between the basement membrane of the epithelium
and the stroma.
It is an acellular layer that is approximately 10micrometers
thick and it consists of randomly orientated collagen fibrils
located within a glycosaminoglycan ground substance. It is
smooth anteriorly where it faces the basement membrane and it
merges posteriorly with the less densely compacted collagen of
the corneal stroma.
Breast feeding
Mothers who are breast
feeding should wait three months after they have finished
breast feeding prior to undergoing laser eye surgery.
Broad beam laser
Historically a lot of the
original excimer
lasers were broad beam lasers. These have largely been
replaced by scanning slit beam lasers or else by flying spot
lasers.
Bulbar conjunctiva
This is that
portion of the conjunctiva
that covers the globe up to the edge of the cornea
at the limbus.
Button-hole flap
This is a lasik
flap complication where the corneal flap has a central hole in
it. In this rare circumstance the excimer
laser treatment is deferred, the flap is allowed to heal
for about 3 months and it may then be re-fashioned or else a
lasek
strategy may be adopted.
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C
Cardiac Pacemaker
The
presence of a cardiac pacemaker in a patient is not a contra-indication
to laser corrective eye surgery. If other forms of ophthalmic
surgery are to be performed under topical anaesthesia then
they can also be carried out in this situation.
Calibration
This is the process
whereby a laser is tested before a treatment session is
started to ensure that the laser is emitting the correct
amount of energy.
Carotenoids
These are the
substances that make up the protective yellow pigment at the
macula.
There are three important carotenoids namely lutein,
zeaxanthin and meso-zeaxanthin. The latter is found
exclusively at the macula.
Lutein is converted to meso-zeaxanthin in the macula
but this conversion from dietary lutein is only 50% efficient
and it is also enzyme dependent and some people may be
deficient in the necessary enzyme. These pigments filter the
damaging blue light whose cumulative damage over many years
results in age-related
macular degeneration. The essential carotenoids may be
obtained together in only one particular dietary supplement
which is known as Macushield. This supplement is available
exclusively from eye-care professionals. The density of the
protective pigments at the macula
in any individual may be assessed using an instrument known as
the macuscope.
Cataract
A cataract is a clouding
of the crystalline
lens that is sufficient to blur the vision. cataracts
have various causes and can occur at any age although they are
most common in the ageing population. Nowadays cataract
surgery affords the opportunity to correct the patient's
vision by implanting an intra-ocular
lens of the appropriate power for the eye being treated.
The vast majority of cataract operations carried out by our surgeon
are performed as a topical day case procedure (see also our Eye
Motion education centre and our PDF files on
cataracts
for more information).
Centration
Very efficient high
speed tracking devices ensure that which work using iris
recognition software work in conjunction with the modern excimer
lasers to ensure that the laser treatment is correctly
centered at all times on the patient's visual
axis. The Bausch & Lomb Technolas system that is used by Ardfallen Eye Clinic is
fitted with an extremely fast tracking system. See also tracking
system below for more information.
Chalazion
This is the medical
term for a cyst in the eyelid. It occurs due to blockage in
one of the orifices of a meibomian
gland and when the secretion of the gland builds up then
this results in a swelling in the eyelid. Occasionally these
will resolve spontaneously but they often require a surgical
operation to remove them. The specific operation is called an
Incision & Curettage and it is generally performed as a
local anaesthetic procedure. If a chalazion becomes infected
then they can be exquisitely tender and it is then called a stye.
Chalazions are much more common in patients with blepharitis
(see blepharitis
above for more information).
Choroid
This is the vascular coat
of the wall of the eye and is located between the sclera
(which is outside it) and the retina
(which is inside it). It is the posterior part of the uvea.
Ciliary body
This
is that part of the uvea
that connects the iris
and the choroid.
Ciliary
sulcus
This is the area in front of the zonules
and the peripheral crystalline
lens capsule and behind the iris.
A posterior chamber intra-ocular
lens may be secured here if there has been a posterior
capsule tear during a lens
extraction operation.
Clear lens
extraction
In this operation a patient's crystalline
lens is removed and an appropriately powered intra-ocular
lens is implanted thereby correcting the patient's refractive
error.
Collagen
This is the most abundant
protein in the body and it makes up 71% of the dry weight of
the cornea.
It provides the structural backbone of the cornea
by making up, along with the proteoglycan matrix, the bulk of
the connective tissue between the corneal cells which are
known as keratocytes.
Collagen
diseases
These conditions affect the fibrous protein of
connective tissues and bones. They are a contra-indication
to most corneal operations (including laser surgery) as
healing is both deficient and unpredictable.
Computer vision syndrome (CVS)
This
term is used to describe the situation where people get tired
sore eyes as a result of using a computer screen (see our Eye
Motion section for more information).
Concave lens
This is a lens
that has a minus power as it defocuses and they are used in optical
aids to correct myopia.
Conductive
Keratoplasty (CK)
This surgical procedure is used to
treat presbyopia.
Conductive keratoplasty utilises a radio-frequency probe to
place a pre-determined pattern of spots on the cornea
which result in a steepening of the central cornea thereby
increasing its power to provide a reading correction. The
pattern of the spots placed on the cornea is determined by the
surgeon using a nomogram
(see also our PDF files on CK).
Confocal microscopy
This is an investigative technique that provides real
time non-invasive live tissue images of corneal tissues. It is
very useful to assess various aspects of corneal healing. This
investigative tool is one of the many sophisticated machines
that we have at our disposal at the Ardfallen Eye Clinic.
Congenital
nystagmus
Nystagmus is an involuntary movement of the
eye which results in a degradation of acuity.
Congenital nystagmus which is present from birth is a contra-indication
to corrective laser eye surgery. This condition is commonly
seen in ocular and oculo-cutaneous albinism.
Conjunctiva
The conjunctiva is
a thin, transparent mucous membrane which lines the inner
surface of the eyelids (where it is known as the tarsal
conjunctiva) and the anterior portion of the sclera
(where it is known as the bulbar conjunctiva). It is also
found in the superior & inferior fornices which are the
spaces between the superior & inferior eyelids and the
eyeball.
Conjunctivitis
This term is used to
describe infection or inflammation
of the conjunctiva.
Consent form
This is
a legal document that a patient must sign prior to undergoing
any form of surgery. It is essential that the patient is given
and absorbs educational material (either as an information
booklet, a teaching DVD or from a web-site) to be able to give
a proper informed consent. All of these are provided at the
Ardfallen Eye Clinic. This then enables the patient to make a
fully informed
decision whether they wish to consent to the proposed
treatment or not.
Consultation
This is the
thorough examination that a patient undergoes to assess the
state of health of their eyes as well as their suitability for
treatment. All the patients of the Ardfallen Eye Clinic are
assessed by our consultant
ophthalmologist at the initial consultation.
Our service is entirely consultant directed from the initial
consultation
right through their entire treatment pathway until their final
discharge. At no point in this process is any decision made by
an optometrist or a technician as it is in many other centres
and we pride ourselves on this point.
Consultant
Ophthalmologist
An ophthalmologist is a highly trained
doctor who specialises in treating diseases of the eyes. An
ophthalmic surgeon is an ophthalmologist who has been trained
in ophthalmic surgery. Our surgeon
is on the specialist register and obtained his CCST (i.e.
certificate of specialist training) from the Royal Academy of
Medicine in London as well as a Fellowship in Ophthalmology
from the Royal College of Surgeons in Dublin.
Contact Lenses
This is a
small lens
that is placed directly on the surface of the eye and it acts
as an optical
aid to correct refractive
errors. A bandage contact lens is a non-optical lens that
is used to accelerate corneal healing. We recommend that
contact lenses are removed for a period prior to the initial
consultation,
optical
work-ups and treatments as they can alter the shape of the
cornea.
With soft lenses we recommend a non-wear time of 1 week and
for hard lenses a non-wear time of 2 weeks. See also our Eye
Motion education centre for more information.
Contact lens
intolerance
This is where a contact lens wearer finds
that it becomes difficult to wear their lenses after a certain
period of time.
Contact lens
trial
This is where contact
lenses are tried out in a person to assess whether they
can tolerate wearing lenses but also to assess if the vision
is good with the correction in the contact
lenses. This may be done to simulate certain visual
outcomes for corrective eye surgery candidates (e.g. in
intended monovision
see below).
Contra-indications
This
term is used to refer to any condition that renders a patient
unsuitable for a particular treatment whatever it may be.
Contrast
sensitivity
This is the ability to detect the
differences between any viewed object and the background
against which it is viewed. It declines naturally with age. It
may also be reduced by forms of corrective eye surgery such as
corrective laser eye surgery.
Convergence
This is the ability
to turn both eyes inwards as the object of interest is brought
closer to the eyes. This enables the fovea
of each eye to remain fixed on the object being viewed.
Convex lens
This is a
lens that has a positive power and it increases the power and
they are used in optical
aids to treat hyperopia
and also an extra addition to provide a reading correction (as
in bi-focals
to treat presbyopia).
Cornea
This is the
transparent layer of tissue on the front of the eye that
provides two thirds of the focusing power of the human eye. It
has a number of layers form the front to the back which are
known as the epithelium
(and its basement membrane), Bowman's layer, the stroma,
Descemet's membrane and the endothelium.
It is the cornea that is re-shaped by the excimer
laser in corrective laser eye surgery.
Corneal ectasia
This term
describes an outward bulging of the cornea
and it may occur when the cornea has been thinned too much by
ablating too much corneal stromal tissue with the excimer
laser. This very rare complication is avoided by ensuring
that there is sufficient corneal tissue by carefully measuring
its thickness both before and during excimer
laser surgery using a pachymeter.
Corneal
erosion
Erosion of the cornea
may occur for a number of reasons including dryness, trauma
and in a pathological condition known as recurrent corneal
erosion syndrome. Corneal erosions are very painful until they
heal as the cornea
is a highly innervated structure.
Corneal flap
This is the flap
of tissue that is fashioned with either a microkeratome
or else with a femtosecond
laser during a lasik
operation.
Corneal
graft
This is where diseased corneal tissue is replaced
with donor tissue. A corneal graft may be a full thickness
graft or else with a partial thickness technique. The medical
term for corneal grafting is keratoplasty.
Corneal haze
This
term refers to a situation where the normally transparent cornea
becomes opacified to varying degrees. It may be the result of
an infiltration of inflammatory cells, a build up of fluid
(i.e. known as corneal oedema), scar tissue or a deposition of
foreign material such as drug deposits. Most forms of haze
will clear given adequate time and treatment. Occasionally
however permanent haze or scarring may develop.
Corneal rings or
inlays
These are little ring segment that can be
inserted into tunnels in the corneal stroma.
They are now used in the treatment of astigmatism,
myopia
and keratoconus
as well as in post laser keratectasia. The tunnels into which
they are inserted can be fashioned either mechanically or else
with the use of a femtosecond
laser. They work by causing a flattening of the cornea after
they have been inserted.
Corneal thickness
The
thickness of the cornea
is measured using an instrument known as a pachymeter
and it is described it terms of micrometers.
It is essential to perform this measurement in both the
planning stage of treatment and also during the performance of
excimer
laser surgery to prevent the complication of corneal
ectasia.
Corneal
topography
This is the measurement of the shape of the
cornea
and the shape can then be displayed in a colour coded map. The
Ardfallen Eye Clinic not only has the capacity to measure
surface topography but also has the machinery to measure
corneal aberrations (using the Zywave in combination with the Orbscan) as well as posterior corneal topography (using the
Pentacam).
Corneal ulcer
This
is an ulcer on the corneal surface and they may be quite
superficial or quite deep depending on the causative
pathology.
Corrective eye
surgery
This is another term for refractive eye surgery
(see below).
Cryotherapy
This is where a
freezing probe is used to treat weak areas in the retina
by creating adhesions (i.e. scarred connections) between the
choroid
and the overlying retina.
Crystalline
lens
This is the lens in the human eye. When it becomes
sufficiently cloudy to blur vision this is known as a cataract.
The clear lens may be removed in an operation to correct a refractive
error where an appropriately powered intra-ocular
lens is the implanted into the patient's eye.
Curvature
This term is used to
describe the amount/degree of curvature of the cornea.
Customised
ablation
This term is used to describe a Wavefront
guided treatment of a refractive
error with the excimer
laser. The laser is then programmed using information
derived from measurements made with a Wavefront
scanning device to treat not only the basic refractive
error but also any aberrations that the patient's cornea
has. All out excimer
laser treatments at the Ardfallen Eye
Clinic are Wavefront
guided with information derived from the Zywave and the Orbscan combined with the refractive data derived from the
initial consultation
and the optical work-up. This information is then programmed
into the Zyoptix treatment calculator software package and a specific ablation
profile is designed for each individual eye being treated.
The purpose designed computer file is then referred to as a shot
file. This shot
file is then inserted into the computer controlling the excimer
laser to deliver the customised
ablation to that particular patient's eye.
Cylinder meridian
In
optics this is the line that is the symmetrical centre of a
curved optical surface and it is a measure of astigmatism.
Cycloplegic
refraction
This is an examination of the eye to measure
the refractive
error while the accommodation
of the eye has been paralysed with a topical Cycloplegic agent
(i.e. Cyclopentolate 1%). It is an essential part of the
initial consultation.
This is why patients should not drive themselves when they
are coming in for their first appointment and why our
secretarial staff always counsel patients of this on the
telephone when they are making their first appointment.
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D
Debridement This is the term for
removal of tissue or else of a foreign body from a wound or
tissue surface (e.g. the cornea).
Decentration
When
an eye is being treated with an excimer
laser the centre of the ablation should exactly coincide
with the centre of the pupil
and /or the visual
axis. If this is not the case then this is referred to as
decentration. When this occurs then is results in various
visual symptoms such as glare
or monocular double vision (which is known as diplopia).
Delayed
healing
This is where a treated eye takes longer than
the usual time to heal after any refractive procedure.
Descemet's
membrane
This is the layer of the cornea
that is situated between the stroma
and the endothelium.
It varies from 5-10 micrometers
in thickness and is the basement membrane of the endothelium.
Microscopically it consists of an anterior banded layer and a
posterior non-banded layer. It increases slightly in thickness
during life but this accumulation seems to be limited to the
posterior non-banded layer.
Detached retina
This is
where the retina becomes separated from its normal attachment
to the back of the eye. It is a very serious condition which
requires a surgical procedure to place it back into its normal
position. If a retinal detachment has previously been treated
successfully then this is not necessarily a contra-indication
to refractive
surgery. However, as it is very unpredictable as to what forces are being transmitted into the vitreous gel when a suction ring is applied to the eye, then lasik is definitely contra-indicated in post retinal detachment repair eyes. It may be possible to perform a lasek treatment on such eyes. It may also be possible to safely perform a phaco-emulsification operation on such eyes.
Deturgescence
This term
refers to the state of relative dehydration that the cornea
is normally maintained in by the pumping action of the endothelium
which pumps aqueous fluid out of the cornea against the
pressure gradient of the intra-ocular
pressure.
Diabetes
Diabetes can affect the
eye in a number of different easy. Glaucoma,
cataracts
and infections are more common in diabetics than they are in
non-diabetics. Diabetes can result in disease of the retina
and this is known as diabetic
retinopathy. This is often investigated with fundus fluorescein
angiography and can be treated with retinal laser treatment.
These lasers operate in a thermal mode and emit light in the
blue-green part of the electro-magnetic spectrum. In diabetic
people in whom their disease is well controlled then they may
be suitable candidates for some form of refractive
surgery.
Diabetic
retinopathy
This is the term that is used to describe
the retinal problems that occur in Diabetes. In early phases
of the disease the retina
may be entirely healthy. The retinal problems happen as a
result of alterations in the circulation. Screening of
diabetics for the development of retinopathy and treating it
early can have a major protective effect on the vision in this
patient group. At the Ardfallen Eye Clinic we use the Zeiss Visucam retinal camera to perform retinal photography when examining all our patients. As this camera is enabled to perform fundus flourescein angiography it is a very useful tool when screening diabetic patients as well as patients with age-related macular degeneration.
Diffractive
optics
Diffraction occurs when light waves are abruptly
interrupted by an edge (such as the pupil)
and it results in a degradation of the quality of the image
being viewed. The light rays are bent at the edge of the
obstruction and this results in the light spreading outside
the geometric image of the target being viewed and this causes
blurring.
Diffuse lamellar keratitis or
DLK
This is where inflammation
occurs between a lasik
flap and the underlying stromal
bed. It is effectively treated with topical steroids but
occasionally it is necessary to re-float the corneal flap and
irrigate the interface to clear the inflammation.
It is caused by white blood cells migrating into the interface
between the corneal flap and the stromal
bed. The most common cause is constituents of the
patient's own tear
film. This condition is also known as "Sands of the Sahara
Syndrome".
Dilation
This is where a patient's
pupil/pupils
are dilated for examination purposes using drops.
Dioptre
This is the unit that is
used to measure the refractive power of a lens.
1 diopter is equal to the reciprocal of the focal length of
the lens expressed in meters. It is written in terms of
capital D and is positive for a converging lens (i.e. convex
lens) and negative for a diverging lens (i.e. concave
lens).
Diplopia
This is the term that is
used to describe double vision. It usually occurs due to a
problem with alignment of the two eyes and is then called
binocular diplopia
which may be horizontal or vertical or a combination of both.
If it occurs in only one eye (e.g. due to a corneal scar or a
cataract
or for some other cause) then it is referred to as monocular
diplopia.
Disposable
contact lenses
These are soft contact
lenses which are discarded after they have been worn for
the designated period of time for which they were designed to
be worn. This may be daily or monthly. Soft contact lenses
should not be worn for a full week prior to the initial consultation
or prior to a refractive
surgery procedure.
Dizziness
Dizziness or a sense of
unbalance can be an occasional transient symptom after any refractive
surgery procedure. It generally subsides fairly quickly
after a period of neural
adaptation.
Dominant
eye
Every individual has one eye that is dominant and
this eye would be used in aiming a gun or focusing a camera
with the viewfinder. In myopic
patients who are in the presbyopic
age-group the dominant eye would be fully corrected for
distance whereas the non-dominant eye would have a slight under-correction
to allow the patient to read smaller print with that eye. The
two eyes are then used together such that the patient has good
binocular acuity for both near & for distance. This is
known as monovision.
In hyperopic patients who are in the presbyopic
age-group the non-dominant eye can have a slight over-correction
while the dominant eye is fully corrected thereby again
allowing the patient to have good binocular acuity for both
near & for distance. This is then known as blended
vision.
Drainage
angle
This term refers to the part of the anterior
segment of the eye where the root of the iris
and the edge of the cornea
meet. At this angle there is a specialised area of tissue
which is known as the trabecular
meshwork. It is through this tissue that aqueous fluid
leaves the eye to enter the venous system. In normal eyes and
in myopic
eyes this angle is quite open whereas in moderate-high grade
hyperopes
it can be quite narrow. This can result in their being at a
far greater risk on angle closure Glaucoma
(see Glaucoma
and also our Eye
Motion section for more information). The technique of
inspecting the dimensions of a patient's drainage angle is
known as gonioscopy. This allows it to be graded in terms of
its degree of openness. The drainage angle is also referred to
as the anterior chamber angle. See our Eye
Motion education centre for more information.
Driving
It is important after any
refractive
surgery procedure to wait until your surgeon tells you if
your acuity
is at the standard required to legally drive.
Dry eye
This term is used to
describe the situation where the tear producing system does
not produce an adequate tear
film to maintain the health of the eye. After laser
surgery the tear
film can be reduced for a variable period of time and
patients require support with topical tear replacement until
their own tear
film production returns to normal. The period of time that
the tear
film is deficient is longer in older individuals and also
tends to be more prolonged in females than in males. The
reason why it is reduced is due to alteration in corneal
innervation and also because the cells near the corneal limbus
are temporarily impaired when a suction ring has been used in
fashioning a corneal flap with a microkeratome.
At Ardfallen Eye Clinic all our laser eye surgery patients are
routinely put on tear
film replacement therapy until their tear
film recovers. See our Eye
Motion education centre for more information.
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E
Ectasia
This is a progressive
corneal thinning. See corneal ectasia above.
Emmetropes
This term describes
people who do not have any significant refractive
error.
Emmetropia
This is the term for
the absence of any significant refractive
error. A person with emmetropia does not require any optical
aids to have good acuity.
Achieving emmetropia or at least near emmetropia is the aim
with refractive
surgery unless the desired outcome is different (e.g. with
monovision
or blended
vision).
Endophthalmitis
This is an
infection inside the eye. It is fortunately a very rare
complication of intra-ocular surgery as it can result in the
loss of the vision or even of the eye itself if it is not
successfully treated immediately it is recognised. This
requires the use of intensive antibiotic therapy both inside
the eye, systemically and with frequent topical therapy as
well. Prevention of endophthalmitis with pre-operative broad
spectrum topical antibiotics, pre-operative cleaning of the
peri-ocular skin with a diluted iodine solution and the
addition of a broad spectrum antibiotics to the fluid used
during the surgery as well as meticulous attention to
sterility have reduced this complication to very low levels
(i.e. <0.1%).
Endothelium
This is the single
layer of cells at the back of the cornea.
This monolayer is essential to the maintenance of corneal
clarity as it maintains the state of relative corneal
deturgescence. If the cell population drops below a critical
number then corneal clarity is threatened. In this
circumstance the patient will require this cell layer to be
replaced with a corneal grafting technique.
Endothelial cell
counts
This is where the number and configuration of
the endothelial cell population is assessed. As there is a
critical number below which the population cannot drop to
maintain corneal clarity this can be a very important test. It
can be performed with either a contact instrument (e.g. a
confocal microscope) or else with a non-contact optical
instrument. The cell population is described in terms of the
number of cells per square mm and also in terms of the shape
of the cells as well as their size (i.e. their morphology).
Enhancement
This
term is used to describe extra excimer
laser treatment that may be required to fine tune a
patient's treatment as a secondary procedure if there is a
significant residual refractive
error after the primary treatment. It is usually done some
months after the primary treatment thus allowing any residual
refractive
error to stabilise prior to undertaking enhancement
surgery. At the Ardfallen Eye Clinic we do not charge for any
enhancements that are required within one year of the primary
treatment. It is important to be aware of other centres that
quote a "from price" for primary treatments as these prices
never include the cost of an enhancement. Nor indeed do they
include the cost of any follow-up care in many instances. It
is vital for any person who is considering corrective eye
surgery to enquire as to what is the enhancement rate at that
particular centre for their particular level of refractive
error. At the Ardfallen Eye Clinic we have an overall
enhancement rate of only 2-3% for laser refractive
surgery which is in line with the enhancement rate for the
best centres worldwide.
Epi-lasek
This term describes the
technique where the epithelium
is peeled back prior to the underlying tissue being treated
with the excimer
laser. A special epithelial debrider is used to perform
this task. After the laser treatment the epithelial sheet is
then replaced and a bandage contact lens is placed on the eye.
Epithelial
in-growth
This describes the situation where corneal
epithelial cells migrate and grow underneath a lasik
corneal flap. This can result in a melting process occurring
in the corneal flap itself. This complication is avoided by
meticulous attention being paid to cleaning out any debris
under the corneal flap at the end of surgery. Occasionally
despite the best care being taken cells may still manage to
migrate under the corneal flap. This may require the flap to
be lifted and these cells to be removed before the flap is
placed back into position. If there are only a very small
number of cells and they subsequently do not exhibit active
growth then they can stabilise and not require any further
treatment.
Epithelium
This is the layer of
cells on the front of the cornea
and conjunctiva.
The tear
film sits on these cells and thereby provides a good
optical surface which is essential to achieving good acuity.
This layer in the cornea is about 6-8 cells deep with the more
superficial cells being flattened while the cells become more
columnar as they get closer to their basement membrane.
Binding of these cells to their basement membrane is critical
and if it is deficient then recurrent corneal erosions may
occur. It is constantly being replaced by the body just like
the skin cells. The nursery for the stem cells for the corneal
epithelium
is situated at the corneal limbus.
Any defect in the corneal epithelium
can be very painful. A bandage contact lens can be very useful
in promoting healing of the epithelium. It is this cell layer
that is peeled back out of the way prior to the underlying
tissue undergoing ablation with the excimer
laser in the lasek
and epi-lasek procedures.
Epitheliopathy
This term is
used to describe any disease or condition which results in a
disorder of the corneal epithelium.
Excimer
The term excimer
is an acronym for EXCIted diMER which is a molecule consisting
of two unstable identical simpler molecules that emit light on
combining and splitting upon excitation by an external
electrical force.
Excimer
laser
This in an Argon/Fluoride laser that emits a beam
of ultra violet light that is capable of removing microscopic
amounts of tissue from the cornea. The removal of this tissue
is known as ablation. At the Ardfallen Eye Clinic the excimer
laser that is used by our surgeon is a Technolas
laser which is a flying spot excimer laser which is manufactured by Bausch & Lomb.
Exophoria
This is a tendency for
the eyes to turn outwards and it is usually the result of weak
convergence. It can result in the patient experiencing
difficulty with close work. It can be assisted with the use of
prisms in the near correction which makes close work more
comfortable.
Exotropia
This is the term used to
describe a manifest divergent squint and it is usually
accompanied by the presence of amblyopia. If the angle of the
squint is of significant magnitude and it is associated with
moderate-dense amblyopia then this is a contra-indication
to refractive
surgery.
Eye
drops
These are drops that are used to deliver medical
treatment to the eye. In the usual formulations they contain
extra ingredients such as carrier vehicles and preservatives.
Patients may react badly to some of these extra ingredients
especially the preservatives with up to 15% of most population
groups being allergic to the preservatives. In this
circumstance preservative free drops become very useful.
Eye patch or
shield
These may be used after different forms of eye
surgery to protect the eye as it heals. Eye patches are also
in occlusion therapy in the treatment of amblyopia.
Eye pressure
testing
This is a common standard test to check the intra-ocular
pressure. The test is also known as tonometry and the
various devices that are used to perform this test are known
as tonometers. At the Ardfallen Eye Clinic we use a number of
different tonometers such as the Tonopen, the Goldmann
tonometer and the dynamic Pascal tonometer.
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F
Far
sightedness
This is the commonly used everyday term
used to describe the medical condition of hyperopia.
Femtosecond
A
Femtosecond is one quadrillionth of a second.
Femtosecond laser
A
Femtosecond laser is a silent bladeless computer guided laser that de-laminates corneal tissue. This new generation of
lasers can be used in various corneal applications to cut
corneal tissue without the use of a blade. In this way they
can be used to fashion a flap for lasik
surgery, to cut the cornea
in various types of corneal grafting techniques (both
penetrating and lamellar), to perform arcuate keratotomies in
the treatment of astigmatism
and to form corneal tunnels prior to the insertion of corneal
rings or inlays. In lasik
they can confer a slight advantage in that no blade is
required although it is not entirely proven that they are any
safer than a microkeratome
when it is used by an experienced and properly trained corneal
surgeon. As these lasers are quite expensive if patients opt
for a blade free treatment then it will be a more costly
procedure for them. The Femtosecond laser that we currently use at the Ardfallen Eye Clinic is the Intralase.
Final
Fit
This is the propriety software package that is
designed and provided by Nidek
to the surgeons who use their excimer
laser system in alliance with their Wavefront
scanning device (i.e. the OPD
scan). The data derived from the OPD
scan is combined with the findings from the initial consultation
and the optical work-up. This then allows the surgeon to
design a customised
ablation for each individual eye that is being treated.
Our surgeon uses his personalised nomogram
to design the ablation profiles and these are directly loaded
into the computer on the excimer
laser in what is called a shot
file. The combination of the Nidek
OPD
scan, the Nidek
excimer
laser, the Nidek microkeratome
and the use of the Final
Fit software is referred to as the Navex platform.
Firemen
People who wish
to enter the fire service as a career have to have a certain
level of acuity to qualify. This can be achieved with refractive
surgery. The visual requirements can be checked on the
fire service web site (i.e. at www.irishfireservices.com). See
also occupation below.
Fixation
This term is used to
describe the ability to maintain an object of interest on the
fovea
of each eye. During excimer
laser eye surgery there is a fixation target that patients
are required to look at during the course of the treatment. At
Ardfallen Eye Clinic we provide patients with a set of
instructions to assist them in doing this during their
treatment. The tracking
system on the excimer
laser is capable of compensating for the normal very small
movements that the eyes make when fixating a target.
Flap
During a lasik
operation a very thin layer of predetermined thickness is
fashioned on the cornea
to create a corneal flap. The flap is designed in such a way
that it has a hinge which maintains its attachment to the
cornea and it can then be folded out of the way so that the
underlying stromal
bed tissue can be treated with the excimer
laser. Once the treatment is complete it can then be
replaced back into its original position. Accurate replacement
is ensured by initially placing a number of fiducial marks on
the eye prior to fashioning the flap. A flap can be fashioned
using a microkeratome
or else with a femtosecond
laser. Complications can occur with either technique and these
include a free flap (i.e. where the hinge becomes separated
from the cornea), a partial flap (i.e. where the flap is not
completed throughout the entire intended course for the flap)
or a buttonhole flap (i.e. where the flap has a defect in the
centre). In the case of a free flap if the fiducial marks were
adequate it can be replaced into its original position after
the excimer
laser treatment is complete and a bandage contact lens can
be used to ensure that it heals in the correct position. With
partial flaps and buttonhole flaps the flap is replaced, the
excimer
laser treatment is deferred, the flap is allowed to heal
for a period of time and then a new flap can be fashioned and
the excimer
laser treatment can then be applied.
Flap hinge
This is the point
where the corneal tissue remains attached after the flap has
been fashioned by whatever technique is used. It can be
designed to be either nasal or else superior. There are
various theories as to which location is better but a review
of the literature would show that either position is good if
the flap is correctly fashioned in the first instance.
Floaters
The largest
space in the eye is the vitreous cavity which is filled with
the vitreous humour or gel. This is normally clear and
colourless. However, it can only undergo a limited repertoire
of change during life and this consists of liquefaction in
which it separates into solid and liquid components. As the
vitreous is a gel these can float into the visual
axis. They can then cast a shadow on the retina
and they are then perceived as a floater. This is known as an
entoptic phenomenon because it is generated within the eye.
This process can be exaggerated especially in a large myopic
eye. In this case the vitreous can separate from the normal
attachment that it has around the optic nerve head. It is
normally only loosely opposed to the retina
between here and its anterior attachment in an area known as
the vitreous base. The large floater generated by its
separation from around the optic nerve head is known as a
Weiss ring. Once this occurs the vitreous then begins to
detach itself from the retina
up to its attachment at the vitreous base and this process is
known as a posterior vitreous detachment (see our Eye motion
education centre for a dynamic explanation of posterior
vitreous detachment).
Fluctuating vision
In the
first few weeks after corrective laser eye surgery it is not
uncommon for the vision to fluctuate. This phenomenon will
settle after this time as the healing process takes place.
Fluorescein
Fluorescein is a dye that has widespread use in
ophthalmology. It can be used topically to stain the cornea
where its property of fluorescence allows the state of health
of the tear
film and the corneal epithelium
to be assessed. Fluoresecence is that property where a
material will emit light in the green part of the
electromagnetic spectrum when it is stimulated by a light of a
slightly shorter wavelength (i.e. in the blue portion of the
spectrum). The dye is taken up by diseased and damaged corneal
epithelial cells and these can then be easily seen using a
blue filter on the slit lamp. This is then known a fluorescein
staining. A Goldmann tonometer uses a blue light to cause
flurosecein to fluoresce in the measurement of intra-ocular
pressure. Fluorescein is also seen to be diluted by
aqueous if there is a leaking wound in the eye in what is
known as a positive Siedel test. It is also used to assess how
well a contact lens is fitting the eye. Intravenous sodium
fluorescein is combined with serial retinal photography to
study the dynamics of the retinal circulation. This is known
as Fundus Fluorescein Angiography (or FFA).
Flying spot laser
This is a type of excimer laser. The Technolas excimer laser is a type of flying spot laser that is manufactured by Bausch & Lomb. It is the type of laser that is currently used by our surgeon to treat patients of the Ardfallen Eye Clinic.
Focimeter
A focimeter is a device
that is used to measure the optical strength of an optical aid
(i.e. glasses or a contact lens) in terms of dioptres of
sphere, dioptres and axis of cylinder as well as dioptres and
orientation of any incorporated prism. These can be mechanical
or more commonly nowadays they are automatic.
Focus
A focus is that point at which
light rays meet. If light rays focus correctly on the retina
then the image is clear and the visual
acuity will be good.
Forme fruste
keratconus
This term is used to describe keratoconus
in its very early stages and this is an absolute contra-indication
to laser eye surgery. This is best detected using optical
measuring devices such as corneal topography, a Pentacam
or else with a confocal microscope. All of these devices are
available at the Ardfallen Eye Clinic.
Fovea
This is the centre of the
macula (see below).
FRCSI
This is the term for a doctor
who has attained the higher medical degree of a Fellowship in
the Royal College of Surgeons in Ireland. Our surgeon has an
FRCSI in ophthalmology. He subsequently was a lecturer in
ophthalmology at that institution and has acted as an examiner
in the Fellowship examination for the college.
Fuch's corneal dystrophy
This is a disease
where the corneal endothelium
becomes diseased with a loss of cells and alteration in their
morphology. It is a contra-indication
to laser eye surgery. If the cell loss proceeds to the point
where the cornea
becomes cloudy then it can be an indication for corneal
grafting.
Fundoscopy
This is the term that
describes examination of the retina
or fundus to ensure that it is healthy. In particular it is
important to ensure that there are no weak areas of retinal
degeneration that may predispose the patient to developing a
retinal detachment. At the initial consultation
drops are used to dilate the pupil
to ensure that the full extent of the retina
may be inspected. If this is not done then the patient has not
been fully assessed. Every patient of the Ardfallen Eye Clinic
has a dilated fundoscopy at their initial consultation.
As the drops used to do this blur the vision all our patients
are advised on the telephone when booking their appointment
not to drive themselves for this examination. It should also
be pointed out that although tumours in the eye are very rare
failure to correctly examine the eye could result in a
potentially fatal lesion being missed.
Fundus fluorescein
angiography
This is the term for the investigation
where fluorescein
dye is used to examine the retinal vessels (see fluorescein
above). Other types of dye are also used to examine the
retinal circulation (e.g. indocyanine green or ICG).
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G
Gas
permeable contact lenses
This is a hard contact lens
that is specifically designed to allow oxygen to penetrate
through it to nourish the cornea
and thereby prevent it being starved of oxygen. As they as a
hard lens they should be left out for at least two weeks prior
to an initial consultation
or prior to any form of corneal corrective eye surgery. If an
implant technique is being used they can be worn until a few
days prior to the surgery.
Ghosting or a ghost
image
This is where a faint second image is seen
alongside the object being viewed. This can occur in the
setting of uncorrected astigmatism
as well as with other ocular problems such as a corneal scar
or opacity in the crystalline
lens.
Glare
This is
where a star burst effect or a flaring is perceived by the
patient when looking at bright lights or objects and these can
be particularly noticeable at night (e.g. when viewing
oncoming headlights while driving). It can occur if there is
persistent haze in the cornea
after laser eye surgery but it is generally a short lived
early symptom in this situation. It can also occur with
multifocal intraocular lenses due to their diffractive optical
design.
Glaucoma
This is
a term that describes a disease which is an optic neuropathy
(i.e. disease of the optic nerve) where there are
characteristic defects that develop in the visual field and is
often but not always associated with an elevation of intra-ocular
pressure. The damage that occurs to the optic nerve
results in the nerve head becoming excavated (and this is
known as cupping of the nerve). This is the most common form
of the disease and it is known as Primary Open Angle Glaucoma
(or POAG). Monitoring of the disease is based on serial
examination of the optic nerve, the visual fields and the
retinal nerve fibre layer. All these parameters have to be
carefully and regularly assessed. At the Ardfallen Eye Clinic
we have our own Humphrey visual fields machine (which is the
recognised gold standard for assessing visual fields) as well
as a GDX VCC retinal nerve fibre layer analyser. In addition
it is vital to monitor intra-ocular
pressure and this is done with three different measuring
devices (namely the Tonopen, Goldmann tonometer and the Pascal
dynamic tonometer). An instrument that measures IOP is known
as a tonometer. A further factor which can confound the
clinical picture is the central corneal thickness (i.e. CCT)
and we also measure this in all our Glaucoma
patients using an ultrasonic pachymeter.
It has been proven in well designed international clinical
trials that reducing the intra-ocular
pressure affords protection to the vision in all Glaucoma
patients and this is done with topical eye drops initially.
Recently a laser technique known a selective laser
trabeculoplasty (i.e. SLT) has been introduced and this very
effectively lowers intra-ocular
pressure. SLT has now gained acceptance as both a
secondary and also possibly a primary effective treatment to
lower intra-ocular
pressure. Occasionally when the intra-ocular
pressure cannot be controlled with either drops and/or SLT
then it becomes necessary to perform Glaucoma
drainage surgery to control the IOP.
The other form of
primary Glaucoma
is known as Primary Angle Closure Glaucoma
(or PACG). This occurs in patients who have a narrow drainage
angle which closes off when their pupil
dilates in dimmer lighting conditions. This tends to be
limited to hyperopes.
Secondary forms of Glaucoma
also occur (e.g. secondary to trauma or uveitis as well as
other conditions). See our Eye Motion section for further
information on Glaucoma
of all types.
Globe
This
term is often used to refer to the eyeball.
Goldmann tonometer
This
is one of the devices that is used to measure intra-ocular
pressure.
Gritty
eye
A feeling of a gritty eye is most commonly a result
of a reduction in the tear
film. After laser eye surgery this is generally a
transient phenomenon. See dry eye above.
Guarantee
As with any other form
of surgery it is not possible to provide a guarantee with
ophthalmic surgery. It is possible however, on the basis of
previous results to provide a realistic expectation of the
potential outcomes and once the patient has been provided with
adequate information to provide an informed consent then
treatment can proceed on that basis. At the Ardfallen Eye
Clinic we endeavour to provide as much information as possible
to assist patients in making these decisions. We do this in
the form of information packs, teaching DVDs, printouts from
textbooks as well as our web site.
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H
Haloes
The perception of haloes
around lights, particularly at night when the pupil
has dilated, is generally a short lived transient symptom
following laser corrective eye surgery. At the Ardfallen Eye
Clinic we measure every potential refractive
surgery candidate's pupil
at three different light settings with the Procyon
pupilometer. This then enables our surgeon to design their
treatment to take account of their pupil
size in lower light level (which is known as scotopic)
viewing conditions. He can then adjust the transition zone to
be at least 1mm larger than the pupil
in scotopic light levels. In this way haloes are not a
troublesome issue after laser corrective eye surgery. They can
also occur with the use of multifocal intra-ocular
lenses due to their diffractive optics design. However,
this is not usually a troublesome symptom unless the patient
has very large scotopic pupils and if that is the case then
they would not be an ideal candidate to receive a multifocal
implant.
Hard contact
lenses
Hard contact lenses are used to correct higher
grades of astigmatism
than soft contact lenses. They can do this as the tear
film acts as a bridge between the posterior surface of the
lens and the cornea
especially in areas where the corneal surface is irregular (as
it can be in astigmatic corneas). Soft contact lenses cannot
do this as they closely appose the surface of the cornea.
Hard lenses can also be used to correct early keratoconus
patients after they have progressed to the stage where their
acuity is poor with a spectacle correction. Hard contact
lenses should not be worn for 2-3 weeks prior to an initial consultation
for refractive
surgery of any kind. They should also not be worn for the
same period of time prior to laser corrective eye surgery.
They can be worn, providing they were left out for 2-3 weeks
prior to the initial consultation
and optical work-up, up to a few days prior to an implant
technique.
Hay fever eye
drops
These are often discontinued for a short period
of time after laser corrective eye surgery. Our surgeon or
practice nurse will advise you as to when you may/should
recommence using them after your surgery.
Haze
Haze is a term used to describe
healing tissue or scar tissue that is visible on examination
with the slit lamp. It most commonly affects lasek
or epi-lasek patients in the first few weeks-months after
surgery. However, it is usually very mild and clears up within
a short period after the surgery. It can be graded as to how
dense it appears on examination. With grade 1-2 haze the
patient may experience little if any visual symptoms in its
presence. With higher grades of haze (i.e. grades 3-4) the
patients will experience some glare
at night and their vision will simulate the effect of looking
through frosted glasses or dirty spectacle lenses. The
presence of haze may require the use of mild topical steroid
drops to accelerate its resolution.
Headaches
Headaches are a not
uncommon but only a short-lived transient symptom after any
form of refractive
surgery. They generally resolve after a few days. When
they are still present it is useful to limit certain visual
tasks such as watching television or prolonged close work
(i.e. reading or using a computer). In general they only last
a few days and then they subside.
Healing
Healing is the process by
which the body recovers or repairs itself following any
insult. This would include any form of surgery. It is
important for patients to understand that all biological
tissue has to undergo this period of recovery and that
different individuals heal at different rates. At Ardfallen
Eye Clinic we ensure that we monitor our patients during their
healing period and that we offer them support as this process
evolves.
Hereditary
This term is used to
refer to those conditions that are passed down along a family
lineage from one generation to the next. When a patient's
history is being taken they will be asked of there is any
condition (either ocular or systemic) that is known to be
passed down through their own family. In the setting of
ophthalmology this is particularly relevant to Glaucoma
and macular degeneration but there are also many other
hereditary conditions so care should be taken to give our
medical staff as full a history as is possible.
Herpes simplex
keratitis
This is an infection of the cornea
caused by the herpes simplex virus. The virus remains dormant
in the tissues and can re-emerge if there is any insult to the
cornea
(e.g. surgery). Due to this possibility it is a contra-indication
to laser corrective eye surgery. The infection can result in
varying degrees of corneal scarring with resultant
affectations of visual
acuity. If the scarring is very severe the eye may require
corneal grafting surgery. Some patients require long term
systemic anti-viral therapy to maintain the virus in a latent
state. This strategy can also be taken with patients who have
had herpes simplex keratitis if they are undergoing cataract
surgery.
Herpes zoster
ophthalmicus
This is an affectation of the eye by the
varicella or chickenpox virus. Chickenpox represents the first
encounter that the patient has with the virus and this is
manifested by a disseminated vesicular body rash of varying
degrees of severity. It tends to be much more florid if the
primary infection occurs in the adult age-group. There may
occasionally be lesions affecting the conjunctiva
or cornea
in the primary infection. The virus then remains in a latent
state in a sensory nerve ganglion and it may become
re-activated later in life and this is then referred to as
herpes zoster. The cornea
can be affected and it commonly results in markedly diminished
corneal sensation. This is known as neuro-trophic keratitis
and in this situation the cornea
can undergo mild to very severe forms of ulceration and
melting. Zoster can also result in varying degrees of uveitis
and elevation of intra-ocular
pressure.
HIV
This is
an acronym for infection caused by the Human Immunodeficiency
Virus. Infection with this virus is an absolute contra-indication
to any form of corrective eye surgery.
Higher order
aberrations
This term refers to the optical
irregularities of the eye other than the conventional optical
errors of power (i.e. in terms of dioptres) of sphere, power of cylinder and axis of cylinder. A conventional (which is
referred to as a plano) correction of these three components
only (i.e. one defocus and two astigmatic) does not provide as
good quality a visual outcome as one that also corrects for
the higher order aberrations. At the Ardfallen Eye Clinic all
our laser corrective eye surgery patients have a Wavefront
correction which is personally designed by our surgeon. This
is done with Wavefront
data derived from measurements which are made with the Zywave aberrometer in conjunction the Orbscan . These are then manipulated with Zyoptix treatment calculator software provided by Bausch & Lomb
to the users of their excimer
laser system along with our surgeon's own personalised nomogram.
Higher order aberrations cannot be measured without the use of
an aberrometer. If a patient is considering undergoing refractive
surgery at any centre then they should ensure that they
will receive a Wavefront
designed customised
ablation and that the surgeon designing it has experience
in this area. They should also question as to what system is
being used to derive the measurements required to design the
treatment. If the answers to these questions are not
satisfactory then it is likely that they will not be receiving
the best quality and most modern treatment with the current
technology that is available. A treatment that is based on
measurements made by an optometrist with no personalised input
from an experienced refractive surgeon is definitely not of
the same standard as one that has an experienced surgeon's own
personal input.
Hypertension
This term means
an elevated pressure in a system. Ocular hypertension relates
to raised intra-ocular
pressure (see Glaucoma
above). Whether the pressure is damaging the eye or not is
determined by assessing the visual fields and measuring the
state of health of the retinal nerve fibre layer. These
services are provided for our patients at the Ardfallen Eye
Clinic.
Hyperopes
These are people who
have hyperopia
(see below).
Hyperopia
This term is used to
describe the condition of long sightedness. In a hyperopic eye
the light rays are focused beyond the retina.
hyperopes
eyes are often smaller in length or else the cornea
may be flatter than the eyes of emmetropes. Earlier in life
lower grades of the refractive
error may be overcome by using accommodation.
With optical
aids a convex (i.e. converging) lens is used to focus
light sharply on the retina
and thereby provide good visual
acuity. It can also be corrected with the excimer
laser. However, it is not possible to treat successfully
as high grade of hyperopia with the laser as it is with levels
of myopia.
In the level of errors that are treatable the laser re-shapes
the cornea
to increase its power. In hyperopes
who are in the presbyopic
age-group a blended
vision strategy may be used. Moderate to higher levels of
hyperopia can be corrected using implants with or without lens
extraction (see below). Residual refractive errors of lower
grade hyperopia can then be suitable for treatment with the excimer
laser (see also our PDF files on corrective eye surgery as
well as our Eye Motion education centre for more information).
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I
Implants
In ophthalmic surgery
this term is used to describe various different types of
intra-ocular lenses (see our PDF files on intra-ocular lenses
for more information).
Incision
This is the medical term
for cutting a part of the body. This is done to provide access
to a space that has a wall. An incision on the eye is required
to gain access to the inside of the eye. This type of surgery
is called intra-ocular surgery. Occasionally partial thickness
incisions are used (e.g. arcuate keratotomies to treat astigmatism).
Induced
astigmatism
There are various techniques that are used
to correct astigmatism.
These include excimer
laser surgery, arcuate keratotomies, toric implants or
combinations of these techniques in certain cases. Any levels
of astigmatism
that were not present prior to any form of treatment are
referred to as induced astigmatism.
Infection
An infection
is where the body is attacked by a pathogen (i.e. a virus, a
bacteria or other agent). Any form of surgery carries the risk
of a possible infection. With intra-ocular surgery special
care is taken to avoid any possibility of infection and as a
result infection rates with this surgery are extremely low. An
infection inside the eye is known as endophthalmitis (see
above).
Inflammation
This is the term used to describe the physical
reactions that the body makes to various stimuli such as
trauma or infection. Signs of inflammation
include pain, redness, swelling, heat and reduction/loss of
function (i.e. vision in the case of the eye).
Informed decision
This
is the term that is used when a patient, who has been provided
with as much information as is possible about a particular
planned procedure, then makes a decision whether they decide
to proceed with that procedure. If they do decide to proceed
then they sign a consent form and provide an informed consent.
At the Ardfallen Eye Clinic we endeavour to provide the
information required to make a fully informed decision via
information packs, teaching DVDs and our web site.
Infusion
This term is used to
describe when a fluid is run into a space. Infusions used in
eye surgery are designed not to result in damage to any
intra-ocular structure. Antibiotics are included in these
infusions to prevent or at least reduce the risk of possible
infection.
In situ
This
term means that something is in place.
Insulin
This is the drug that is
used to treat insulin dependent diabetes.
Intacs
This is the term for corneal
rings or inlays (see above).
Interface debris
This term
is used to describe particles or debris that is present in the
interface between a corneal flap and the underlying stroma
after laser corrective eye surgery. Interface debris is
usually not visually significant. On occasion it may be of
some significance (see diffuse lamellar keratitis and
epithelial in-growth above). Once meticulous care is taken
with washing out the interface at the end of lasik
surgery then there is normally no interface debris of any
significance.
Interpalpebral
fissure
This is the space between the eyelids. It is
usually almond shaped.
Intra-stromal corneal
rings
See corneal rings or inlays above.
Intralase
This is the type of femtosecond laser that is used by our surgeon to generate corneal flaps on patients who are having lasik surgery.
Intra-ocular lens
(IOL)
This is the term used to describe various types
of intra-ocular lenses that are implanted into the eye during
an intra-ocular surgical procedure. They are often referred to
as implants (see our PDF files on intra-ocular lenses).
Intra-ocular
pressure (IOP)
This refers to the pressure within the
globe of the eye. If the pressure in the eye was not greater
than atmospheric pressure then the eye would not remain
inflated. The intra-ocular pressure unit of measurement is mm
of Mercury (i.e. mmHg) above atmospheric. It is measured using
a device which is called a tonometer. Most of these tonometers
work on the basis of flattening (or applanating) the cornea.
It has now been proven that intra-ocular pressure tends to be
higher in people who have thicker central corneas as measured
using a pachymeter.
The normal range for IOP is thought to be 14-21mm Hg. Raised
IOP can be associated with retinal nerve fibre layer damage
(which is evidenced by thinning of that layer with retinal
nerve fibre layer analysis) and resultant visual field loss or
even blindness in with advanced Glaucoma.
Therefore monitoring of raised IOP is essential to protect
vision.
Intra-ocular
surgery
This is surgery that is performed on tissue
that is contained within the globe. It therefore requires an
incision to gain access to that space. The incision/incisions
used may vary in size but would all be very small with modern
techniques. This would include such operations as cataract
surgery and implant techniques.
Iris
This is the most anterior portion
of the uvea.
It is the coloured ring of tissue that is situated in front of
the crystalline
lens and behind the cornea.
The hole in the centre of the iris
is the pupil.
iritis Iritis
This term means
an inflammation
of the iris.
Irregular
astigmatism
This is a refractive
error where the astigmatic error cannot be described in
terms of two regular axial corneal meridians at 90 degrees to
each other. The corneal shape is different along the principal
meridians which may be separated by angles other than 90
degrees. This type of cornea
is most accurately measured using a Wavefront
scanning device, a Pentacam
or else a corneal OCT. To correct such an error with excimer
laser would require a customised Wavefront
correction.
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K
Kerato
This is a prefix that is
applied to the cornea.
Kerato-conjunctivitis
This
is the term that describes an infection or inflammation
that affects both the cornea
and the conjunctiva.
Keratoconus
In this
condition the shape of the cornea
becomes more progressively more irregular with time. It
develops an irregular astigmatism
that can be initially corrected with optical
aids but as it progresses it eventually requires surgical
intervention. Corneal rings or inlays can be implanted into
the corneal stroma
to stabilise the cornea and reduce the astigmatism.
Once the astigmatism
has progressed beyond a certain stage then the only technique
that produces good results is corneal grafting (i.e. keratoplasty
see below). keratoconus
is nearly always bilateral and is asymmetrical (i.e. one eye
is more advanced). Its rate of progress varies between the
eyes and also between different individuals.
Keratotomy/keratectomy
This is the term for
an incision that is made in the cornea
with a view to treating corneal astigmatism
(see arcuate keratotomies above).
Keratitis
This is the term that
describes an infection or inflammation
of the cornea.
Keratocytes
These
are the cells that are normally found in the ground substance
of the corneal stroma
in between the collagen fibres. They can be visualised using
confocal microscopy.
Keratometry
This is the term
used to describe the measurement of the curvature of the cornea.
The instrument originally used to perform this task was a
keratometer. This is generally now performed using corneal
topography, a Pentacam
scan or a Wavefront
scan.
Keratoplasty
This is the term
used for a corneal graft of whatever type that is (i.e. full
thickness or partial thickness etc.).
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L
Lacrimal glands
These are
the tear producing glands with the main gland being located in
the upper outer eyelid and orbit and the accessory glands
being located in multiple areas in the upper & lower
conjunctival cul-de-sacs. The lacrimal glands produce the
aqueous layer of the tear
film.
Lacrimal tear drainage
system
This is the system that drains away the tear
film. There are two little entrance holes to the system
which are known as the lacrimal puncta. These are located at
the medical end of both the upper & the lower eyelids.
There is then a narrow channel (which is known as a
canaliculus) which leads from each punctum towards a structure
known as the lacrimal sac which is located medial to the eye
and lateral to the side of the nose. In the majority of people
the two canaliculi join together as a common canaliculus prior
to joining the lacrimal sac. The lower end of the lacrimal sac
turns into a canal which is known as the naso-lacrimal duct.
This passes through the side wall of the nose to open at its
lower end in the inferior nasal meatus. Hence if we cry our
nose also runs.
When there is a blockage of the lacrimal
system then this results in a watery eye. This is known as
epiphora and it may be either a functional blockage or else a
total physical blockage. The degree of patency of the lacrimal
system may be tested by performing a lacrimal sac wash-out.
When the system is freely patent on performing a sac wash-out
then enlargement of the lower punctum with a 3-snip operation
is frequently curative of the epiphora. If the system is
patent only when a fairly high level of hydro-static pressure
is required to pass fluid (usually saline) through it, then
this is referred to as functional epiphora. In this
circumstance then the system can be intubated (i.e. a tube is
placed in the system) and the tear
film then passes through the system around the tube. The
tears are attracted into the system around the tubing by
capillary attraction. When the system is completely blocked
then the level of blockage may be shown using radio-opaque dye
and x-rays in a test which is called a dacryo-cystogram. If
the blockage is shown to be in the naso-lacrimal duct then an
operation which creates a communication between the lacrimal
sac and the nose can alleviate the watering and this operation
is called a dacryocystorhinostomy (or a DCR as it is commonly
referred to).
Lamellar
keratoplasty
This is the term that is used to describe
a corneal graft where only a partial thickness of corneal
tissue is replaced with donor tissue. This may be superficial,
mid-stromal or a deep lamellar graft.
Lasek
This is an acronym for Laser
Assisted sub-epithelial Keratomileusis (see our notes on lasek
term information for more information).
Laser
This is an acronym for Light
Amplification by Stimulated Emission of Radiation. There are
many different types of lasers that are used in ophthalmology.
They may work by different types of an affect that they have
on tissue (e.g. this may be a thermal affect or it may be a
cool beam affect). All the lasers used require considerable
experience to use to their best effect.
Laser eye surgery
Various
types of laser can be used to perform a variety of different
types of surgery on the human eye (e.g. an excimer
laser is used to perform corrective eye surgery).
Lasik
This is an acronym
for Laser Assisted In-situ Keratomileusis (see our notes on
lasik term information as well as our Eye Motion education
centre for more information).
Lazy eye
The medical term for this
is amblyopia (see above).
Lens
A lens is a transparent material that alters the path
of light waves as they pass through it. Depending on their
shape they bend light in different directions (see concave
lens and convex
lens above). The amount by which they divert the light
from its original path depends on their power which is
measured in dioptres. The lens in the human eye is referred to
at the crystalline
lens.
Lens
extraction
In ophthalmic surgery this refers to removal
of the crystalline
lens. This may be done because the patient has a cataract
or as part of a refractive
surgery procedure. When it is part of a refractive
surgery procedure it may be referred to as a clear lens
extraction or else a refractive lens exchange (i.e. REFLEX).
In the presbyopic
age-group it is referred to as a presbyopic
lens exchange (i.e. prelex).
Lesion
This is the
medical term that refers to any structural change that occurs
in a body part as a result of injury or disease. It can
therefore be used to refer to various different processes
(e.g. an ulcer, a scar or a tumour which if cancerous is then
referred to as a neoplastic lesion).
Leucoma
This is the term for a
corneal scar. They can vary in their density, location and
depth within the corneal tissue as well as in their secondary
features (such as degree of vascular in-growth or associated
degenerative features). They result in the cornea
in the area of the scar becoming opaque. This occurs due to
dense collagen fibres being laid down which are orientated at
different angles to each other and there is often varying
degrees of blood vessel in-growth (which is known as
neo-vascularisation) associated with these dense scars.
Limbus
This is the term
that describes the area between where the clear cornea
and the white tissue of the globe which is called the sclera.
Logmar
This is an
alternative scale for describing the visual
acuity (i.e. alternative to the most commonly used Snellen
visual
acuity scale). Logmar has certain advantages in that it is
decimalised and so can more easily be used in statistical
analyses.
Long
sight
Long sightedness is the common term for hyperopia.
Low vision
aids
These are optical
aids that are specifically designed to assist a patient
with age related macular degeneration with viewing reading
material.
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M
Macula
Macula is the term used to
describe the central area in the retina
where the photoreceptors are most densely packed. In this way
they are able to provide the best possible acuity with this
part of the retina.
The absolute central part of the macula is known as the fovea.
Macular
degeneration
This disease is more commonly known as age
related macular degeneration (i.e. ARMD). As it affects the
central part of the retina
it is the central vision that suffers damage as a result. It
is of two types which are atrophic and neovascular. They both
damage vision but to varying degrees. They are only
occasionally treatable although the newest available treatment
with intra-vitreal injections of anti-angiogenic agents does
appear to offer much better potential outcomes. Investigation
of the condition requires retinal imaging techniques such as
fundus fluorescein
angiography and retinal OCT. It is much more common in people
who have a positive family history of ARMD and in people of
advanced years. Factors that are known to worsen the condition
include smoking and prolonged exposure to the damaging effects
of blue light. This is why the use of carotenoids
appears to be protective against this cumulative light damage.
Macular
oedema
This is where fluid or swelling (which is known
as oedema) affects the macular area in the retina.
As it is this area that provides the best acuity then this has
a deleterious effect on the vision. It may be visualised with
FFA or retinal OCT. Both topical and systemic carbonic
anhydrase agents are effective in accelerating its resolution
in certain cases.
Magnify
This is the term used to
describe how the image of an object is enlarged when viewed
through a magnifying lens (i.e. a positive power or convex
lens).
MB BCh
These
are the letters that indicate that the person who has these
letters after their name has qualified from university as a
Bachelor of both Medicine & Surgery.
Meibomian glands
See
meibomian gland secretions below for more information.
Meibomian
gland secretions
The meibomian glands are located
within the tarsal plates of the upper & lower eyelids.
These glands secrete the lipid layer of the tear
film. This is the outer layer of the tear
film which both prevents its evaporation and also provides
a surface tension so that the tear
film remains stable on the corneal surface.
Microkeratome
This is a high
precision surgical device that is used to fashion a corneal
flap in preparation for surgery to the stromal corneal tissue
that lies beneath the corneal flap. This is generally laser
corrective eye surgery with the excimer
laser but a corneal flap may also be fashioned with a view
to a deep lamellar keratoplasty technique. The instrument is
placed carefully over the eye. It has a suction ring attached
to it and once suction is applied the instrument is firmly
secured in the correct position. The IOP is checked and once
it has risen to an adequate level to make the eye firm a motor
is activated and the micro-incision blade traverses the cornea
and fashions the corneal flap. It then returns to its home
position, the suction is discontinued and the instrument is
removed from the eye. It should be pointed out that in the
hands of an experienced fully trained corneal surgeon (such as
our surgeon) that this is an extremely safe procedure. The
overall flap complication rate in such hands is of the order
of <0.5% (see our section on lasik
term information and also our Eye motion section for more
information).
Micrometer
A micrometer is one
thousandth of a mm (i.e. .001mm). It is still occasionally
referred to as a micron.
Micron
One thousandth of a
millimetre (see micrometer above).
Microstriae
This is the term
for tiny folds or wrinkles which occasionally occur in a
corneal flap. They are most commonly of no visual
significance. Infrequently they can cause a loss of the
sharpness of the vision. They are visible only by examination
with the slit lamp.
Microsurgery
This term refers
to surgery that is performed with an operating microscope
being used to visualise the tissue which is being operated on.
All intra-ocular surgery is microsurgery.
Monovision
This term refers to
the refractive target where the desired outcome is for the
patient to have one eye focused for near visual tasks and the
other eye set for distance. This usually applies to myopic
patients who are also presbyopic.
In this circumstance the dominant eye is fully corrected
whereas the non-dominant eye is under-corrected to retain a
pre-determined amount of myopia.
This enables patients to see clearly both for near & for
distance using both eyes together. As both eyes are being used
together it requires the patient to have good stereoacuity to
achieve the best result with monovision. A visual simulation
can be demonstrated to patients during their initial consultation
to see if they would accept the very slight diminution in
their distance vision. A contact lens trial of the potential
outcome can be tried if there is uncertainty after that. To
most patients in this category monovision is extremely useful
and the distance vision is described as being excellent. It
should also be remembered that there is always a period of neural
adaptation to the new visual situation. This can vary in
its duration so perseverance after surgery is essential. In
hyperopic patients who are also presbyopic
a similar refractive target is referred to a blended
vision. Here the dominant eye is fully corrected as in
monovision while the non-dominant eye is over-corrected to
induce a pre-determined amount of myopia.
As with monovision both eyes are then used together to see
clearly both for near & for distance. Monovision can also
be achieved with implants by selecting a different power in
each eye.
Monofocal
This term is applied to
a lens that focuses light to one single focal point. In
ophthalmic surgery it may be applied to an intra-ocular
lens that is designed to correct the distance vision only
after surgery.
Morbidity
This is the term that
is used to describe the various affects that any condition has
on a person.
Myopia
This
term is used to describe the condition of short sightedness.
In a myopic
eye the light rays are focused in front of the retina.
Myopia can be graded in terms of its magnitude in terms of
dioptres. In moderate to high grades of myopia the eye is
often larger than in emmetropia. With optical
aids a concave (i.e. diverging) lens is used to focus
light sharply on the retina
and thereby provide good visual
acuity. Low to moderate grades of myopia can be corrected
with the excimer
laser. In the level of myopic
refractive errors that are treatable the laser re-shapes the
cornea
to decrease its power. In myopes who are in the presbyopic
age-group a monovision
outcome may be the desired refractive target. Moderate to
higher levels of myopia can be corrected using implants with
or without lens extraction. Residual refractive errors of
lower grade myopia can then be suitable for treatment with the
excimer
laser (see our PDF files on corrective eye surgery).
Myopia is associated with an increased risk of a number of
ocular conditions (i.e. cataract,
Glaucoma,
& retinal detachment). The risk of a potential detachment
can be assessed by careful fundoscopy with a dilated pupil.
This should be performed on every patient at their initial consultation.
Any weak areas that are identified on the retina
could then be treated to try to prevent a detachment occurring
at a later stage. These areas can be treated with a thermal
laser treatment or else with a freezing probe (i.e.
cryotherapy). Both these approaches are designed to create
adhesions/connections between the choroid
and the overlying retina.
In this way they should not be able to separate subsequently.
See also our Eye Motion section for more information.
Multifocal
This term
is used to refer to intra-ocular lenses that are designed with
multiple refractive zones to focus light from both near &
from distance on the retina.
This provides patients with good unaided acuity for both near
& for distance post-operatively. However, as they work
utilising diffractive optics, they can cause some glare
and haloes to be perceived especially around lights at night.
Careful patient selection for these types of IOLs is therefore
important. When suitable patients receive these implants they
are delighted with their visual result. See also our notes on
intra-ocular
lens term information.
Multiple
sclerosis
Occasionally patients with MS may be suitable
for corrective eye surgery. It depends on the stage of the
disease they have and also on its rate of progression. The
overall suitability can be determined at the initial consultation.
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N
Nasal hinge
This describes where
a corneal flap is designed to have its hinge located in the
nasal as opposed to the superior position.
Navex
This is the registered name for
the combined Nidek excimer
laser; the Nidek
OPD
scan and the Nidek microkeratome
with the Final
Fit software package in the treatment of refractive
errors (see customised
ablation and Final
Fit above).
Nebulas
This term is used for scars
on the cornea
that are translucent to varying degrees. If a nebula becomes
denser and therefore relatively opaque it is then called a
leucoma (see above).
Negative power lens
This
is a concave or diverging lens (see above). Such a lens is
used in an optical aid to correct myopia.
Neural
adaptation
In ophthalmic surgery this term is used to
refer to the process where the brain adapts to a new visual
situation (such as monovision
or blended
vision). It can take many months in some individuals and
therefore it is worthwhile persevering if the desired
refractive target has been achieved after corrective eye
surgery.
Nidek
Nidek is a
privately owned Japanese company that design and manufacture
equipment that is used in the diagnosis and delivery of
treatment in many areas of ophthalmology. It is a highly
innovative company that is recognised worldwide for its
engineering excellence. Nidek has gained approval from the FDA
in the USA for the use of its excimer
laser system in the treatment of refractive
errors.
Nomogram
This is the term for the
particular adjustment that a surgeon makes to any treatment
programme design on the basis of his/her experience with that
particular technique. Our surgeon has his own personalised nomogram
that is based on treating many patients with excimer
laser corrective eye surgery successfully.
Non dominant eye
Every
individual has one eye that is dominant and this eye would be
used in aiming a gun or focusing a camera with the viewfinder.
The other eye is then, of course, referred to as the
non-dominant eye (see dominant eye above).
Nystagmus
These are involuntary
jerking eye movements. They are often associated with poor visual
acuity, strabismus and refractive
errors. This often renders patients with nystagmus
unsuitable candidates for laser corrective eye surgery.
However, they may be suitable for an implant technique
providing that they have adequate visual potential.
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O
Obsessive nature
People who
have a particularly obsessive type of nature do not make ideal
candidates for most forms of elective surgery. Their
expectations may be such that they cannot accept that there
can be no absolute guarantee with surgery.
Occupation
This is an important
consideration in the planning of any refractive
surgery procedure. In correcting any potential candidate
for a particular prospective career it is vital to be aware of
the particular visual requirements for that career. Included
here are links that provide those requirements for the Gardai
(link is www.garda.ie), the Irish military services (link is
www.military.ie) and the fire services (link is
www.irishfireservices.com). At the Ardfallen Eye Clinic we
have successfully corrected many people who have subsequently
joined each of these services having had their vrefractive
errors corrected to meet these required standards.
With implant techniques occupational considerations also
play a major role in selecting the ideal solution for each
individual. For example people who drive a lot at night would
not be ideal candidates to receive a multifocal intra-ocular
lens as the diffractive optics design does cause haloes
which may not be tolerable in this circumstance. By contrast
an accommodating intra-ocular
lens does not cause these problems due to its different
design.
Ocular coherence tomography (i.e.
OCT)
This is an imaging technique that provides
extremely detailed live images of both the anterior
segment and the posterior segment of the eye. This can be
very valuable in both diagnosis and treatment planning.
Ocular
This is the term
that is used to refer to anything relating to the eye. The
Latin word for eye is oculus.
Ocular hypertension
This
term describes the situation where an individual has an intra-ocular
pressure that is elevated above the normal range but does
not have any resulting damage to either their visual fields to
their retinal nerve fibre layer. Patients in this group are
referred to as ocular hypertensives. It has been proven in
well designed international clinical trials that reducing the
intra-ocular
pressure affords protection to the vision in patients with
ocular hypertension. Monitoring of ocular hypertensives with
regular visual field testing and retinal nerve fibre layer
analysis and careful monitoring of the optic nerve head is
critical in the proper care of this cohort of patients. We
have equipment to provide this service at the Ardfallen Eye
Clinic and we now provide the care for a large group of both
ocular hypertensives and patients with Glaucoma.
See Glaucoma
above as well as our Eye Motion section for more information.
OD
This is an abbreviation
for the right eye that is derived from the Latin which is
Oculus Dextra.
Oedema
This is the medical term for
swelling or fluid which has accumulated at a particular
location usually as a result of inflammation,
an allergic response (see allergy above), a vascular event or
else an infection. Its location at certain critical sites can
have quite a deleterious effect on the function of that part.
This is particularly so with macular oedema (see above).
Off axis
This is a term
that is used to refer to the location of a lesion that is not
on the visual
axis.
On axis
This
term refers to the location of a lesion on the visual
axis (see off axis above).
OPD (i.e. optical path difference)
scan.
This is the aberrometer that is designed by Nidek
for use with their excimer
laser. The Wavefront
data derived from the scans performed by the OPD
scan is then loaded into the Final
Fit software package and our surgeon then uses his
personalised nomogram
to design a customised
ablation for each eye of every individual patient for
laser corrective eye surgery.
Ophthalmologist
An
ophthalmologist is a doctor who specialises in the diagnosis
and treatment of the eye and disease of the eye. An
ophthalmologist who is also trained in ophthalmic surgery is
then called an ophthalmic surgeon. It takes many years to
train as an ophthalmic surgeon (see our surgeon).
Optic nerve
This is the nerve
that contains the millions of nerve fibres that transmit the
signals from the photoreceptors in the retina
to the visual area in the brain. Some of the processing of the
signals takes place in the retina
and the rest of this processing occurs in the brain.
Optic nerve
head
This is the portion of the optic nerve that is
visible with various examination techniques at the back of the
eye. Careful examination of the nerve head (which is also
commonly referred to as the optic disc) is done at the initial
consultation
and it can then be monitored over the rest of the patient's
life. This is of particular importance for in diseases of the
optic nerve, in particular Glaucoma
(see above).
Optical
This word refers to light
and its behaviour as well as to the eye.
Optical aids
This is the
term that describes devices that helps to focus light rays on
to the retina
thereby providing clear vision. In particular it is used to
refer to spectacles/glasses and contact
lenses. However, it may also be ascribed to a device that
assists a patient with age related macular degeneration to see
reading material more clearly. It is then known as a low
vision aid.
Optical
axis
This term describes the principal axis where light
rays pass through any optical system. In the eye it is also
referred to as the visual
axis.
Optical
work-up
This is the term used for the series of
investigations that are carried out after the patient's
initial consultation
that will provide our surgeon with the extra parameters that
are required to design a treatment that is most suited to each
individual eye. At the Ardfallen Eye Clinic we have invested
heavily in the most modern and up-to-date equipment that is
currently available worldwide to provide the most modern, most
effective and safest treatment that currently exists. We
constantly seek to stay at the forefront of the technological
development that occurs so rapidly in this exciting area of
medicine.
Optical
zone
This term is used to define the central portion of
the cornea
through which light rays pass along the visual
axis to focus on the retina.
It may also be used in describing the central portion of an ablation
profile that is used to re-shape a cornea
with an excimer
laser in correcting a refractive
error.
Optician
This is the term used to
describe a person who supplies and fits spectacle frames and
contact
lenses but who is not qualified to prescribe either type
of optical aid. When an optician is qualified to prescribe optical
aids then they are referred to as a dispensing optician.
An optician who is qualified to examine eyes and to prescribe
and supply optical
aids is called an optometrist. It should be emphasised
that neither of these terms implies that the individual is
qualified to treat any eye diseases. They are not an
ophthalmologist (see above). Therefore centres that rely on
optometrists to design treatments for patients are certainly
not going to be able to provide as good care as centres where
a fully qualified and well trained ophthalmic surgeon is
involved in the care path from the initial consultation
right through to the point where the patient is returned to
the care of their primary physician (i.e. their general
practitioner or GP). At the Ardfallen Eye Clinic we pride
ourselves in that our surgeon is involved fully in each and
every patient's care path from the start to the final
discharge back to their GP's care.
Optometrist
This is the term
for an optician who is qualified to examine eyes and to
prescribe and supply optical
aids (see optician above).
Orbscan
The Orbscan is a complex instrument that is capable of measuring the optical system of the cornea. It achieves this by using slit scanning technology with an advanced placido disc system. Data derived from the Orbscan is then combined with measurements made with Zywave aberrometer and this data set can then be run through the Zyoptix treatment calculator software to design a shot file for each individual eye's treatment.
Over-correction
This is the
term that is used to describe the outcome where the achieved
amount of correction of a refractive
error is greater than the error that was treated. This may
have been the refractive target that was intended in certain
situations (e.g. in blended
vision corrections in hyperopic patients who are also presbyopic).
In circumstances where it was not the intended outcome the
over-correction may be reversed with the excimer
laser.
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P
Pachymeter
This is a device that
is used to measure the thickness of the cornea.
This is a vital piece of information in designing a treatment
to correct a refractive
error. This may be done with an ultrasound or else with an
optical device such as the Pentacam.
Pachymetry
This is
the process of using a pachymeter
to measure the corneal thickness.
Partially sighted
This
term refers to the situation where a person has a significant
reduction in their vision that is not correctable with either
optical
aids or with any surgical intervention. The person is not
completely blind. However if the degree of impairment is at a
certain level of acuity then the person may be eligible to be
registered with the National Council for the Blind in Ireland
(i.e. NCBI who can be contacted at www.ncbi.ie) and could then
derive whatever state benefits to which they are entitled on
the basis of their handicap. (A link for the government
department of Social Welfare is www.welfare.ie). The cause of
the visual impairment can be many and varied. Common causes
would be age related macular degeneration, Glaucoma,
myopic
retinal degeneration, significant other retinal pathology
(such as advanced diabetic retinopathy) or it may be a
congenital problem (i.e. one which the person was born with as
a result of a hereditary problem/disease).
Pain
Pain is not usually experienced
to any degree after lasik
although patients may feel a very slight degree of discomfort
from the spring/speculum that is used to keep their eye open
during the treatment. Mild headaches are occasionally reported
after lasik
but they are usually only present for a day or two at
most.
After lasek
most patients feel some grittiness and irritation of their eye
for a few days. This is reduced significantly by the presence
of the bandage contact lens that is inserted into their eye
for a few days following the procedure. In addition at the
Ardfallen Eye Clinic we routinely prescribe both systemic
painkillers and sedatives to assist with sleeping after lasek
to help patients through their recovery. Very occasionally
severe pain may be experienced but this is very unusual and
only lasts 12-24 hours.
Pascal dynamic
tonometer
This is a tonometer that measures the intra-ocular
pressure throughout the cardiac cycle. It provides a
quality score for each reading (with scores running from 1 at
worst to 5 at best) as well as the ocular pulse amplitude
(i.e. OPA). People with higher OPAs are more likely to sustain
visual field damage as a result of sustained elevation of
their IOP. At the Ardfallen Eye Clinic we measure IOPs in all
our Glaucoma
patients (and also with Glaucoma
suspects) with three different tonometers (i.e. the Goldmann
tonometer, the Pascal dynamic tonometer and with the Tonopen).
Pentacam
The Pentacam
is an instrument designed and manufactured by a company named
OCULUS. It is a rotating Scheimpflug camera which calculates a
3-dimensional model of the anterior
segment of the eye. The topography and pachymetry of the
entire anterior & posterior surface of the cornea
from limbus
to limbus
are calculated and depicted. It also performs an analysis of
the volume and height of the anterior chamber, calculates the
angle of the drainage
angle as well as deriving densitometry of the crystalline
lens. It is an extremely useful tool in the diagnosis and
management of ophthalmic surgery patients. At the Ardfallen
Eye Clinic we have been using a Pentacam extensively since
2004.
Peripheral
vision
This is the ability to see or be aware of
objects that are not located directly in the line of vision
but are located on either side of that line. This can be
tested using a visual field analyser. At the Ardfallen Eye
Clinic we have our own visual field machine to provide this
service to our patients. The peripheral visual field may be
damaged in certain conditions such as a stroke that affects
part of the visual pathways or the visual centre in the brain.
It may also be affected in certain types of brain tumour (e.g.
pituitary gland tumours) and in this circumstance the visual
field test becomes a very important part of the diagnosis.
Testing may also be performed to assess whether an individual
has an adequate field to be able to drive safely. In the UK
the DVLA proscribe a binocular visual field of 140 degrees
horizontally by 40 degrees vertically as being the legal
standard for driving.
Personalised
nomogram
Our surgeon has developed his own personalised
nomogram for use with the Nidek excimer
laser. This has been developed with experience gained from
treating thousands of eyes with this particular laser. If a
person is contemplating having laser corrective eye surgery at
any centre then they should enquire as to what nomogram
is being used in the design of their ablation
profile. If the operating surgeon has not developed a
personalised nomogram
then they should be asking why that is. Furthermore, if their
treatment is being designed on the basis of measurements made
on machines operated by a technician or optometrist only, then
perhaps they should consider whether they might be better off
being treated at a centre where these parameters are more
favourable. For more information see customised
ablation above.
Phaco-emulsification
This
is the word that is used to describe the most modern method
used for cataract
or clear lens extraction (see our PDF files on cataract
surgery, our specific section on cataract
term information or else our Eye Motion section for more
information). Basically this is a high frequency ultrasound
that liquefies crystalline
lens matter and it is used in conjunction with an
infusion/aspiration system to maintain the volume of the eye
in a steady state during the surgery. The term was derived
from the Greek stem "phako" which means lens.
Phakic
This term means that the crystalline
lens of an eye is in situ. It is the opposite of aphakic.
If an implant is implanted into a person's eye to correct
their refractive
error while their own crystalline
lens is still in situ then the implant is referred to as a
phakic IOL.
Phakic
IOL
This is an implant that is implanted into a
person's eye to correct their refractive
error while their own crystalline
lens remains in situ (see our PDF files on corrective eye
surgery or else our intra-ocular
lens term information section for more information).
Phoropter
head
This is an optical instrument that contains
multiple lenses and therefore can be used in the assessment of
a refractive
error. It can increase the speed of an examination but is
not essential to do this properly.
Photoablation
This is another
term for ablation (see above). It is a non-thermal method of
tissue removal where the UV light emitted by the excimer
laser has a higher voltage than the bonds that hold
molecules together (these are known as van der Waal's forces).
Therefore application of an excimer
laser beam causes the molecules of corneal tissue to fall
apart thereby removing or ablating tissue. When viewed with an
electron microscope tissue treated with the excimer
laser shows extremely precise cuts with zero evidence of
any damage to the tissues surrounding the area treated with
the laser beam.
Photophobia
This is the term
that refers to the situation where a person has an extreme and
unusual sensitivity to light. This can be an occasional but
transient symptom after any form of corrective eye surgery. It
usually resolves with time as the patient becomes adjusted to
the new visual situation (see neural
adaptation above). It can also be a symptom in a number of
ocular conditions (especially in uveitis and ulcerative
keratitis) and it may occur as a side effect of a number of
different systemic medications (e.g. Amiodarone).
Photoreceptors
These are the
specialised neural receptors that are located in the retina
and that detect light rays that are focused on the retina.
They then transmit the signals that pass along the optic nerve
to the visual processing areas in the brain where they are
converted into images.
Photorefractive keratectomy
(i.e. PRK)
This is a form of excimer
laser corrective eye surgery where the corneal epithelium
is first removed prior to the application of the laser beam to
correct the refractive
error. This has largely been replaced by either lasik
or lasek.
Removal of the epithelium
resulted in this procedure being very uncomfortable after the
surgery until the epithelial cells had grown back.
Pilots
Corrective eye surgery may be
employed to meet the required visual standards for acquiring a
commercial pilot's licence. The visual requirements can be
obtained from the aviation authority (web site www.iaa.ie).
The visual requirements for a pilot in the military air
services may be obtained from the following web site-
www.military.ie.
Pinguecula
This is a growth on
the bulbar conjunctiva
(i.e. that part of the conjunctiva
on the globe) that occurs at the limbus
and results from prolonged exposure to the damaging effects of
ultraviolet radiation (i.e. sunlight). Therefore they are more
commonly seen in people who work outdoors or else who have
lived in a sunny climate for some years. If they become a
cosmetic blemish then they are easily excised.
Pinhole
A pinhole is an optical
device that cuts down the light rays entering the eye to a
single beam. This can then be used to measure the visual
potential in any eye providing there is not extensive
pathology present in the ocular media (e.g. an advanced cataract
or severe corneal scarring may prevent the acuity improving
with a pinhole).
Pituitary gland
tumour
Due to its proximity to the junction of the two
optic nerves (which is known as the optic chiasm) tumours in
the pituitary gland compress this area and this results in
characteristic visual field defects. In this circumstance
visual field testing can be an extremely useful diagnostic
tool.
Plano
This term is
used to describe a lens of zero power.
Posterior chamber
This is
the space behind the iris
and in front of the crystalline
lens and the zonular apparatus.
Posterior
vitreous detachment (i.e. PVD)
This is where the
vitreous (see below and also our Eye Motion section for more
information) becomes separated from its normal attachments in
the posterior part of the eye. It is normally firmly attached
around the optic nerve head and anteriorly in an area in the
anterior part of the choroid
which is known as the pars plana. This anterior attachment is
called the vitreous base. With ageing the vitreous can only
undergo a limited repertoire of change. With time it separates
into more solid and liquid components and thereby it loses
volume. When this occurs it pulls away its attachment from
around the optic nerve and this previously attached ring
(which is called a Weiss ring) is seen as a floater in the
eye. Between the optic nerve at the back of the eye and the
vitreous base anteriorly the outside layer of the vitreous
(which is called the vitreous cortex) is normally only loosely
apposed to the retina.
As it separates from the retina
it can stimulate the retina
and this results in the sensation of a flashing light. When it
has fully separated the posterior face of the vitreous floats
in the eye while the anterior part remains attached at the
vitreous base.
In some people, in particular moderate-high
grade myopes, there can be abnormal adhesions/attachments
between the vitreous cortex and the retina
between its attachment around the optic nerve and the vitreous
base. In this setting, as a PVD evolves, these abnormal
attachments can result in the retina
being torn. Fluid can then leak into this hole and cause the
retina
to become detached from the choroid.
Initially only a small localised area of the retina
may be detached but this grows and then the person will
experience a curtain of blackness coming into their visual
field. This then requires a surgical operation to repair the
retinal detachment (see above).
Power
In ophthalmology this term is
used to refer to the power of a lens to bend light (i.e. its
refractive power which is expressed in dioptres). If this is a
minus then the lens being described is a concave
lens and if it is plus then it is a convex
lens. A concave
lens is a diverging lens that is used to correct myopia
whereas a convex
lens is a converging lens which is used to correct hyperopia.
Practice nurse
At
the Ardfallen Eye Clinic we have a full time practice nurse
who carries our emergency mobile phone (number 087 9050249).
Pregnancy
Women should
not undergo laser corrective eye surgery while they are
pregnant or breast feeding. It is best to wait until 3 months
afterwards. The cornea
can change in shape during pregnancy and after delivery.
Presbyopia
This is
the term that describes the reduction in the ability of the
eye to perform close work tasks with increasing age. The usual
age at which this process begins to effect people is in the
early to late 40s. A person who is presbyopic
is referred to as a presbyope. If the person was emmetropic
then they require a reading correction to perform close work.
If they were hyperopic then they would require an extra
correction for near and this may be worn in either bi-focals
or else in varifocal lenses. If they were myopic
then they would require a lesser correction for close work.
Again this may be worn in a bifocal or varifocal format.
Occasionally myopic
presbyopes will actually take their spectacles off and use
their myopia
to focus for near. Presbyopia may also be treated with either
conductive
keratoplasty or else with a presbyopic
lens exchange (see below). In excimer
laser corrective eye surgery a blended
vision strategy may be used in presbyopic
hyperopes
and a monovision
strategy may be used in myopic presbyopes. For a further
description see either our Eye Motion section or else our PDF
files on corrective eye surgery.
Presbyopic
A person with presbyopia
is described as being presbyopic.
presbyopic
lens exchange (i.e. PRELEX)
This is a refractive
surgery procedure where the patient's crystalline
lens is removed with phacoemulsification and it is
replaced with an intra-ocular
lens of predetermined power to correct the patient's refractive
error. When the patient is presbyopic
then the intra-ocular
lens used is either a multifocal IOL or else an
accommodating IOL. In this way both the distance refractive
error and the presbyopia
are both corrected. See our PDF files on intra-ocular lenses
and on corrective eye surgery as well as our Eye Motion
section for more information.
Prism
A prism is defined as a portion
of a refracting medium bordered by two plane surfaces which
are inclined at a finite angle. The angle between the two
surfaces is called the refracting angle. Light rays are
deviated towards the base of a prism. The power of a prism is
expressed in terms of prism dioptres with a prism of one prism
dioptre
producing a linear displacement of 1cm of an object situated
at 1m distance. As prisms have this ability to shift or
displace an image in a linear manner they are used in
spectacle lenses to correct for a squint or to assist a person
who has a tendency for their eyes to deviate from the normal
alignment.
Protocols
In medical terms these
are the sets of rules or guidelines that are followed when
delivering any form of treatment. They are designed to
maintain very high standards and to ensure that every time a
treatment is delivered that safety standards are maintained at
the highest possible levels.
Pseudo-exfoliation
syndrome
This is the name for an ocular condition where
material similar to the capsule of the crystalline
lens is deposited at various locations in the anterior
segment of the eye. This deposition is seen around the
border of the pupil
(where it is known as a papillary ruff), in a discoid pattern
on the anterior crystalline
lens capsule and on the zonules.
It may result in weakening of the zonules
to the extent that the crystalline
lens is seen to shimmer on eye movements when observing
the eye with the slit lamp (this is known as phaco-donesis).
This may then result in surgical difficulties in treating a cataract
with phaco-emulsification. Pseudo-exfoliation syndrome is
associated with an increased rate of early cataract
formation and increased IOP which when associated with
characteristic visual field loss is known as Glaucoma
capsulare.
Pterygium
This a lesion of the
bulbar conjunctiva
that like a pinguecula occurs as a result of prolonged
exposure to the damaging effects of UV radiation. They are
triangular in shape and they can grow progressively from their
initial location on the bulbar conjunctiva
near the limbus
to invade the cornea
in the interpalpebral fissure. With time they may reach the visual
axis and they can then affect the vision. Usually they
would be excised prior to that stage as they are a cosmetic
blemish.
Phototherapeutic keratectomy (i.e.
PTK)
This is where the excimer
laser is used to treat corneal pathology such as scarring
or recurrent corneal erosion syndrome.
Procyon pupilometer
This
is the type of pupilometer that we use at the Ardfallen Eye
Clinic.
Ptosis
This is
the medical term for a drooping of the upper eyelid which
therefore narrows the interpalpebral fissure. It can
occasionally be seen as a temporary feature after an eyelid
speculum or clamp has been used to keep the eye open during an
ophthalmic surgical procedure. It most often occurs in the
ageing population due to a slippage of the muscle that
elevates the eyelid (namely the levator palpebrae superioris).
In this circumstance it can be repaired by surgically
advancing this muscle back to its normal position. Ptosis also
occurs in a congenital form where the levator muscle does not
develop properly. In this setting the eyelid can be elevated
by hitching the muscle to the frontalis muscle in the
forehead.
Punctum
This
is the opening of the tear drainage system (which is known as
the lacrimal system) in the medial portion of each eyelid.
They are also referred to as the lacrimal puncta. In dry eye
disease a plug may be placed into the lower punctum to prevent
the tear
film draining away. In this way the plug can also act as a
supplement to the topical lubricants and render them more
effective. In a watering eye the lower punctum can be enlarged
to assist in drainage of the tears. This procedure is known as
a 3-snip operation (see lacrimal system above for more
information).
Punctal
plugs
These are small silicone or plastic plugs that
are placed into the lower lacrimal puncta and in severe dry
eye disease they may be placed into the upper puncta as well
(see above).
Pupil
The
pupil is the hole in the centre of the iris
which rapidly adjusts its size depending on the intensity of
the ambient lighting conditions. It acts as an aperture to
maximise the acuity.
Pupilometer
This is an
instrument that is used to measure the size of the pupil
in different lighting conditions. At the Ardfallen Eye Clinic
we use the Procyon pupilometer to perform this task.
Pupil size
The
measurement of pupil
size with a pupilometer is an important part of the optical
work-up for corrective eye surgery especially with the excimer
laser. Ensuring that the transition zone of the laser
ablation is larger than the scotopic pupil
markedly reduces the incidence of problems like glare
and haloes after excimer
laser corrective eye surgery.
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R
Radial keratotomy (i.e.
RK)
This was the operation that was originally used to
treat myopia.
It was an incisional technique that allowed the peripheral cornea
to bulge a little and thereby the central cornea
flattened and the refractive power of the cornea
lessened. The number of incisions used was dependent on the
degree of correction required. The central optical zone of the
cornea
was left untouched and the incisions were made with a special
blade or keratome in the mid-peripheral cornea.
As multiple incisions were made in the cornea
RK resulted in the cornea
being weakened and susceptible to rupturing with mild to
moderate degrees of trauma. RK has been replaced by the use of
the excimer
laser to more accurately reshape the cornea
in the treatment of myopia.
Reading
glasses
Reading glasses become necessary for people
when they enter the presbyopic
age-group. There are a nowadays a number of very effective
treatments for presbyopia
(see above and also see our Eye Motion centre for more
information).
Refraction
This is the term that
is used to describe the mathematical description of a person's
refractive
error. It is expressed in terms of power and sign (i.e.
plus or minus) of sphere and power, sign and axis of cylinder.
It is also the word that is used to describe the alteration
that occurs in the path of rays of light as they pass through
a lens. The light rays are bent as they pass through the lens
unless of course the lens is a plano lens (i.e. it is of zero
power).
Refractive
error
A refractive error is an optical error in an eye
whereby light rays are not focused onto the retina
by the refractive media of the eye. The different refractive
errors that a human eye can exhibit are myopia,
hyperopia,
astigmatism
and presbyopia.
Any individual eye can be purely myopic
or else it can have a combination of myopia,
astigmatism
with/without presbyopia.
Alternately it could be purely hyperopic or else have a
combination of hyperopia
with astigmatism
with/without presbyopia.
The refractive error of any eye can be measured manually with
an instrument known as a retinoscope used in conjunction with
trial lenses. This process is called retinoscopy. It may also
be measured automatically with an instrument known as an
auto-refractor. The result is then referred to as an
auto-refraction. See our Eye Motion education centre as well
as our PDF files on corrective eye surgery for more
information.
Refractive
power
This is the amount by which a lens can displace
the path of light rays as they pass through it. It is
expressed in terms of dioptres.
Refractive surgeon
This
is the term that is used to describe an ophthalmic surgeon who
has been trained in and specialises in the surgical techniques
that are used to correct patient's refractive
errors. Usually it takes many years to train in these
techniques and a corneal fellowship is the most appropriate
training scheme to produce a refractive surgeon. Our surgeon
is a trained refractive surgeon who spent a full three years
working in a corneal service. He regularly goes on training
courses to learn and master new techniques as they are
developed and introduced.
Refractive surgery
This
is the term that describes any surgical technique/procedure
that is designed to reduce if not eliminate a patient's
requirement for optical
aids to provide clear vision and good visual
acuity. The principles of these techniques are that
something is either removed (e.g. corneal tissue in excimer
laser surgery) or added (e.g. a phakic IOL) or a
combination of both (e.g. in a presbyopic
lens exchange) to correct the refractive
error being treated. Surgical principles dictate that with
any refractive
error being treated the technique that is used removes the
least possible amount of tissue to achieve the desired goal.
Refractive
target
This is the term that is used to describe the
intended refractive power that is anticipated after any
particular form of refractive surgery. It is most commonly
emmetropia but in certain circumstances a different outcome
may be the desired refractive target. For example in a patient
who is myopic
and is also in the presbyopic
age-group an under-correction
in the non-dominant eye may be the refractive target if a monovision
strategy is being adopted. Conversely in a hyperopic patient
who is in the presbyopic
age-group an over-correction
in the non-dominant eye may be the refractive target if a blended
vision strategy is the treatment plan being designed for
that individual.
Regression
After any type of refractive
surgery a very small percentage of treated patients may
exhibit some regression of their original refractive
error. This is usually only a minor amount of their
original error but very occasionally they can regress to their
pre-treatment error. This is most often seen where the
original error was hyperopia
of a magnitude that would have been better treated with an
implant technique as opposed to an excimer
laser correction. Most examples of minor regression can be
re-treated once the residual refractive error has stabilised.
Re-growth
This is the
term used to describe the natural replacement of tissue.
Regular
astigmatism
This is astigmatism
where the corneal shape is regular and can be described in
terms of two regular axes which are separated by 90 degrees.
This is a treatable refractive
error. It is the opposite of the situation seen in
irregular astigmatism (see above). See also our Eye Motion
section for more information.
Retina
The retina is the light
sensitive layer/membrane at the back of the eye. It is a
highly complex structure that contains the photoreceptors.
Light is focused onto the retina by the optical media of the
eye in emmetropia or else by optical
aids in refractive
errors. Some neural processing occurs in the retina prior
to the signals being transmitted via the retinal nerve fibres
to the optic nerve and then to the visual processing areas in
the brain. It is there that the signals are interpreted and
converted into images (see our Eye Motion section for more
information).
Retinal
detachment
See detached retina
and posterior vitreous detachment above as well as our Eye
Motion education centre for more information.
Retinal holes and tears
These may occur in
the process of a posterior vitreous detachment developing (see
above). They may be sealed with either a thermal laser or else
with cryotherapy. Once they have been adequately sealed off
then they are not a contra-indication
to treatment of a refractive
error.
Retinal
nerve fibre layer (i.e. RNFL)
These are the very fine
nerve fibres in the retina that transmit the signals from the
photoreceptors to the optic nerve. It is in this tissue layer
that the neural damage that occurs in Glaucoma
is clinically obvious. Analysis of this layer is therefore
critical in the care and diagnosis of Glaucoma.
Retinal nerve fibre layer analysis
As the
neural damage that occurs in Glaucoma
is first clinically obvious in this tissue layer analysis of
the health of the RNFL (see above) is critical in the car and
diagnosis of this potentially blinding disease. At the
Ardfallen Eye Clinic we use the GDX VCC to analyse the RNFL in
each and every patient where there is any suspicion of Glaucoma.
Retinoscope
This is
the instrument that is used in conjunction with trial lenses
to measure a person's refractive
error.
Retinoscopy
This is the term
that is used to describe the use of a retinoscope in the
measurement of a person's refractive
error. It may be done without any drops and it is then
called a dry retinoscopy or else it can be performed using
drops to paralyse the person's accommodation
when it is the called a cycloplegic retinoscopy.
Re-treatment
In some cases it
is necessary to perform a further treatment to fine tune a
result after refractive
surgery. These treatments are often referred to as
enhancements. At the Ardfallen Eye Clinic we do not charge for
enhancements that are required within one year of the original
treatment. After that period there will be a nominal charge
that will be fully outlined prior to any treatment being
undertaken. It is vital for any person who is considering
corrective eye surgery to enquire as to what is the
enhancement rate at that particular centre for their
particular level of refractive
error. At the Ardfallen Eye Clinic we have an overall
enhancement rate of only 2-3% for laser refractive
surgery which is in line with the enhancement rate for the
best centres worldwide. We also would undertake an excimer
laser treatment in certain implant surgery cases where the
refractive target is not exactly achieved with the primary
implant surgery. This generally only occurs with higher grades
of refractive
error which would not have been amenable to treatment with
the excimer
laser alone and in these cases we would always counsel the
patient of this possibility prior to undertaking any surgery
in the first instance. All potential costs would be outlined
at the point where a treatment plan was initially outlined to
the patient and prior to their giving a fully informed consent
to any treatment being undertaken.
Risks
Any surgical procedure carries
certain risks. With meticulous care being taken during the
initial consultation,
the optical work-up and the surgery itself these can be
minimised. At the Ardfallen Eye Clinic there is consultant
supervision and input at every stage of the patient's
treatment and we are convinced that this provides the best
possible standard of care currently available worldwide. There
is a full and frank disclosure of the risks (albeit these
being of a very low level) in our educational information and
in our consent form. In this way any potential candidates for
treatment can provide a fully informed
decision prior to their consenting to undergo any form of
treatment.
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S
Scanning slit beam
This is
the term for a type of excimer
laser. The Nidek
excimer
laser system operates with this type of design. This excimer
laser system used in conjunction with Wavefront data derived from the OPD scan to design shot files utilising the Final Fit software package provided by Nidek on the Navex platfrom.
Scar
This is the medical
term that is applied where the healing process in the body
lays down extra fibrous tissue at the site of a previous
insult, be that an injury from trauma or surgery, or as a
result of an infection or an inflammation.
Examples of this in ophthalmology would be in the cornea
following an infection where a faint nebula is the result or
more seriously where a leucoma is the outcome. A further
example would be in the retina
where age related macular degeneration results in a fibrous
scar occurring at the macula
at the burnt-out stage of this disease.
Schlemm's canal
This is the
name for a channel that surrounds the circumference of the
anterior chamber. It is oval in shape and is lined with a
similar type of cell that lines blood vessels in the body.
These cells specialise in the transport of fluid across the
wall of the canal. The inner surface of the canal communicates
with the anterior chamber via the trabecular
meshwork. Its outer wall is contained within the deep
tissues of the limbus.
It is the Schlemm's canal that the carries the aqueous to the
venous system via what are known as collector channels.
Sclera
This is the name
for the white part of the globe. It is made of densely packed
criss-crossing collagen fibres. It forms the posterior five
sixths of the globe. Its anterior junction with the cornea
is known as the limbus.
Sclerotomy
This is a
surgical opening in the sclera.
Sclerotomies are used to perform a vitrectomy (see below).
Scuba-diving
Scuba-diving,
along with other water related sports, should be avoided for
at least two weeks after excimer
laser corrective eye surgery. Our staff at the Ardfallen
Eye Clinic will advise as to any other restrictions in
relation to other procedures or sports.
Selective laser
trabeculoplasty (SLT)
This is the name for a laser
technique to lower the intra-ocular
pressure. It has been shown to very effective in lowering
the IOP without causing any long term damage to the trabecular
meshwork (i.e. the tissue through which the aqueous humour
leaves the eye -see below). See also Glaucoma
above and our Eye Motion section for more information.
Short
sightedness
This is the commonly used term to describe
the refractive
error of myopia
(see above and also see our PDF files on corrective eye
surgery as well as our Eye Motion section for more
information).
Shot
file
This is the computer file that is inserted into
the excimer
laser to deliver the customised
ablation to a patient's eye after it has been designed by
our surgeon with the Zyoptix treatment calculator software from the data derived from the initial consultation
combined with the data from the optical work-up and using his
own personalised nomogram.
Slit lamp
This is the
name for the microscope that is used in the clinical
examination of the eye. It uses a very narrow beam of light to
visualise structures in the eye and to detect any problems
(e.g. cataracts).
Snellen
chart
This is the name of the most commonly used visual
acuity chart that is used to quantify the visual
acuity level. Normal sight is then referred to as 20/20
(i.e. twenty -twenty vision). This means that the person can
see a letter on the chart (which is known as an optotype) at
twenty feet that a normal sighted person should also be able
to see at that distance from the Snellen chart. It may also be
referred to as 6/6 where metres are substituted for feet as in
20/20.
Social
reading acuity
This is the term used to describe an
acuity that is consistent with being able to read social print
(i.e. menus or regular newspaper print) without the assistance
of an optical aid. This can easily be provided along with
excellent distance acuity in presbyopic
patients using various strategies (see monovision,
blended
vision and prelex
above).
Soft contact
lenses
We recommend that soft contact
lenses are not worn for 1 week prior to both the initial
consultation
and the treatment.
Speculum
This is the name for the
small spring or clamp that is used to keep the eyelids open
during treatment. It is not painful although the occasional
person may find it a little irritating at the beginning. They
can also cause very mild eyelid swelling after removal. Very
infrequently there may be a transient droop of the eyelid
after a speculum has been used but this will always resolve
after a short period (see ptosis above).
Sphere
This is the term for the
power of a spherical lens (i.e. either concave or convex) and
it is measured in terms of dioptres.
Sports
Our staff at the Ardfallen
Eye Clinic will advise patients as to what are the
restrictions with regards to participation in various sports
after different procedures (see also scuba-diving above).
Squint
This term is used
in medicine to describe the situation where the two eyes are
not aligned correctly. The optical axes of the eyes may
converge resulting in a convergent squint or they may diverge
resulting in a divergent squint. They are most commonly
treated in childhood and if there has been successful
treatment to prevent amblyopia then the visual
acuity may be very good in adult life. It there has also
been a good outcome of any squint operation then the ocular
alignment may be very good as well. The medical term for
squint is strabismus. Surgery to correct a squint is therefore
referred to as strabismus surgery. In these circumstances it
may be possible later in life to have surgery to correct the
refractive
errors that are often the cause of the squint in
childhood. However, if there is an obvious residual squint
along with poor vision even with an optical aid in one eye
then this would mean that such a person would not be a
candidate for corrective eye surgery.
Stable prescription
Prior to undertaking corrective eye surgery, especially in
younger patients, it is important to be sure that the refractive
error is stable and is not changing. A change of greater
than or equal to 1 dioptre
over 24 months would indicate that the refractive
error was not stable. Most people will have a stable error
in their late teens to early twenties. Past prescriptions will
be very useful if brought along at the time of the initial consultation.
Starbursts
This is
usually a transient effect after excimer
laser refractive
surgery. The visual effect is a blurring of images of
bright light emitting sources with the impression of spikes
radiating out from the centre of the light source. This effect
diminishes as microscopic healing occurs and it eventually
disappears especially when a Wavefront
designed customised
ablation has been used to treat the eye. All our
corrections at the Ardfallen Eye Clinic are Wavefront
designed by our surgeon using the Zyoptix treatrment calculator software and his own personalised nomogram
(see above).
Stereo
acuity
This is the term used to describe the ability of
the two eyes to see things in three dimensions. It is
expressed in terms of seconds of arc with normal stereo acuity
being 40 seconds of arc. There are various techniques for
measuring this and at the Ardfallen Eye Clinic we usually use
the Stereo Fly test. The stereo acuity is usually markedly
reduced in patients who have a squint or who have amblyopia.
This is an important parameter to measure when considering if
a potential candidate for a monovision
or a blended
vision correction will be able to tolerate this
correction. Even with excellent stereo acuity they will still
have to undergo a period of neural
adaptation to achieve the best outcome from such a
treatment strategy. Stereo acuity will also play an important
role in the assessment of a person who may be a candidate for
a conductive
keratoplasty correction of their presbyopia
(see our PDF files on conductive
keratoplasty for more information).
Steroid eye drops
Steroid
drops (either alone or in a formulation combined with an
anti-biotic) are often prescribed in the post-operative
treatment after various forms of eye surgery. Their use is
usually limited to prevent any induced side effects (e.g.
elevation of IOP). It is important that patients are under
supervision when they are using such medication.
Sticky eye lids
If your eye
lids are sticky after corrective eye surgery then they should
be cleaned very gently with a clean piece of cotton wool that
has been soaked in boiled water. The eye can then be dried
with a clean soft tissue. It is important not to use any drops
other that those prescribed for you in the first few weeks
after any form of eye surgery. If you suffer from blepharitis
then this will have been treated intensively in the few weeks
leading up to your surgery.
Stinging eye
It is not uncommon
for the eye to sting after various forms of eye surgery. This
usually only occurs in the immediate post-operative period and
resolves fairly quickly. It is much more common after lasek
and epi-lasek than it is after lasik.
During this period of healing it is very important to avoid
rubbing the eye as it heals. Stinging may also occur on
instilling drops but it is usually mild. If it is more severe
than this you should alert our practice nurse at the clinic
and she will advise you as to what course of action needs to
be taken. A fairly high percentage of people are allergic to
some of the preservatives used in eye-drops. In these patients
we often have to adjust their topical therapy to preservative
free drops and this usually resolves the problem.
Strabismus
This is the medical
term for squint (see above).
Stroma
This is the name of the layer
that constitutes the bulk of the cornea.
The stroma consists of bundles of collagen of uniform size
that extend the width of the cornea.
These are enmeshed in a ground substance consisting of
mucoproteins and glycoproteins. There are also cells which are
known as keratocytes.
Its most densely packed anterior layer is known as Bowman's
membrane. The posterior surface is lined by a membrane which
is known as Descemet's membrane. It is the stromal tissue that
is ablated in excimer
laser corrective eye surgery. Live tissue images of the cornea
can be obtained using confocal microscope. This service is
available at the Ardfallen Eye Clinic and it is an extremely
useful tool in monitoring healing in any patient.
Stromal bed
This term is applied
to that part of the corneal stroma
that is exposed when a lasik
corneal flap is fashioned. This is the part of the cornea
that will be ablated in excimer
laser corrective eye surgery. It is vital during surgery
to measure this stromal
bed once the corneal flap has been fashioned (by whatever
means) prior to any laser energy being applied. In this way it
can be ensured that an adequate amount of residual stroma
remains to maintain corneal integrity and thereby prevent the
possible development of corneal ectasia (see above).
Stye
A stye is an infected
chalazion (see above).
Sunglasses
These are very useful
in the healing phase after any form of corrective eye surgery.
The most useful type to maximally diminish glare
problems is polarised sunglasses.
Swimming
Patients are advised to
avoid swimming for at least two weeks after corrective eye
surgery of any form to prevent the risk of infection. Our
staff at the Ardfallen Eye Clinic will advise patients as to
what are the restrictions with regards to participation in
various sports after different procedures (see also
scuba-diving above).
Swollen eye lids
Puffiness
and swelling of the eyelids after treatment is not uncommon
but it usually resolves very quickly. If a patient is
sensitive to preservatives in the post-operative drops then
they may also develop such problems. In this circumstance they
can be switched over to preservative free drops (see stinging
eye above).
Symptoms
This is the medical term
for what the patient feels as a result of having a disease or
illness or else as the result of some other insult (e.g.
trauma or surgery).
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T
Target light
This is the small
light that a patient is asked to look at while they are
undergoing an excimer
laser treatment. At the Ardfallen Eye Clinic patients are
provided with a specific set of focusing light instructions to
assist them in this. They are also coached by our surgeon both
before and during their treatment.
Tarsal plates
These form the
skeleton of the eyelids thereby giving the eyelid margin
stability. They consist of dense fibrous tissue and contain
the meibomian glands within their substance. The upper tarsal
plate is 10-11mm high while the lower plate is only 3-4mm
high. The meibomian glands open through the eyelid margin
posterior to what is known as the grey line. This is the
junction between the conjunctiva
and the squamous epithelium
(i.e. the skin epithelium) along the eyelid margin.
Tear film
The tear film is the
complex layer of fluid that coats the front surface of the
eye. It is essential in providing a good optical surface and
therefore in allowing a good visual
acuity. It is made up of three different layers. These
from front to back are the lipid layer, the aqueous layer and
the mucous layer. As the posterior mucous layer is intimately
associated with the corneal & conjunctival epithelium
it can be thought of as part of those structures. It lies in
the spaces formed by the front surface of these cells which
have tiny peaks (which are known as microvilli) and valleys as
part of their normal structure. The mucous layer coats the
surface of these cells and thereby provides a smooth surface
on which the aqueous layer of the tear film sits. It also
converts the surface of these cells from a hydrophobic surface
(i.e. one which repels fluid) to a hydrophilic surface (i.e.
one which attracts fluid). This layer which is about 0.02-0.5
micrometers
thick is produced by the goblet cells of the conjunctiva.
It provides stability to the tear film as a whole.
The
bulk of the tear film is made up of the aqueous layer. It
measures about 7 micrometers
in thickness and it is produced by the main and the accessory
lacrimal glands. It is thought that the accessory glands
produce the basal tear secretion while the main gland produces
the reflex tear secretion. The aqueous layer contains absorbed
nutrients as well as enzymes and antibodies produced by the
body to protect the surface epithelium
of the eye. The lipid layer is secreted primarily by the meibomian
glands in the upper & lower eyelids. It coats the
front of the aqueous and provides stability as well as
preventing evaporation of this layer.
In situations where
the tear film id deficient (e.g. in dry eye disease) the tear
film has to be replaced by topical lubricants. If this is not
done then the surface of the eye will dry and this can result
in tiny erosions occurring in the epithelial layer. These can
enlarge or indeed become infected. In addition, as there is a
poor quality optical surface the vision is also compromised.
It also results in symptoms of irritation and grittiness with
foreign body sensation. The eye often appears red with
vascular congestion of the surface vessels and it is commonly
misdiagnosed as conjunctivitis.
When a suction ring has
been used to fashion a corneal flap in lasik
operations there is a period where the tear film is somewhat
deficient and requires replacement with tear drops. This
occurs for two main reasons which are the transient
malfunctioning on the goblet cells located around the limbus
(due to the suction ring being located in this area) as well
as the alteration in corneal innervation following the
formation of the corneal flap. This period of deficient tear
production is transient and it usually resolves fairly
quickly. It is longer in older patients and is also longer in
females that it is in males.
Technolas
This is the excimer laser system that is manufactured by Bausch & Lomb for the correction of refractive errors. It is a flying spot laser and it utilises data derived from the Zywave aberrometer and the Orbscan to deliver customised Wavefront treatments. The shot files that are programmed into the excimer laser are designed with the Zyoptix treatment calculator. This is the type of excimer laser that our surgeon uses in treating patients of the Ardfallen Eye Clinic.
Testimonials
These are the
experiences of past patients of the Ardfallen Eye Clinic which
describe the patient's experience for various forms of
treatment that we have performed for them (please see above
our section on testimonials).
It is very useful for candidates for any form of treatment to
read these and we will provide contact details if requested
for a direct one-one conversation with a past patient if
required.
Tonometer
This is the term for an
instrument that measures the intra-ocular
pressure. This is an essential test in an eye examination.
At the Ardfallen Eye Clinic we routinely check IOP and have
the instruments available to do so with three different
measuring devices. We use the Tonopen, Goldmann and the
dynamic Pascal tonometers.
Tonometry
This is the term used
to describe the measurement of the intra-ocular
pressure and the instrument used to perform this
measurement is called a tonometer (see above).
Tonopen tonometer
This is
a hand held tonometer for measuring the intra-ocular
pressure. At the Ardfallen Eye Clinic we measure the IOP
in all our Glaucoma
patients (and indeed all the Glaucoma
suspects that we review) with three different tonometers (i.e.
the Tonopen, Goldmann and the dynamic Pascal tonometers).
Topical
anaesthesia
Topical anaesthesia refers, in ophthalmic
surgery, to the situation where anaesthesia is achieved with
the use of anaesthetic agents which are applied to the ocular
surface as drops. It is an extremely effective and
non-invasive way to allow very many eye operations to be
carried out while the patient remains completely comfortable.
In this way surgery can often be offered to people who would
otherwise be unable to have the procedure (e.g. an elderly
patient who has a cataract
but whose general health may not allow any other form of
anaesthesia to be used safely). At the Ardfallen Eye Clinic it
is routine for our surgeon to carry out the vast majority of
the procedures available using topical anaesthesia. In the
rare instance where a general anaesthetic is required those
facilities are available at the hospital to which our surgeon
has admitting rights.
Topography
This is the term for
the measurement of the corneal geography. In earlier years
this used only be used to measure the surface of the cornea
but as the technology has advanced there are instruments
available that can map the entire corneal architecture (see Pentacam,
OPD
scan and OCT above). All these types of devices are used
at the Ardfallen Eye Clinic to give us the maximum amount of
information required to treat our patients in the safest &
most effective way possible. We continue to invest in the
latest and most up to-date equipment to provide the best
possible service to our patients.
Toric lens
A toric lens is a lens
that corrects for astigmatism.
Its ability to bend light is expressed in terms of dioptres of
cylinder and the orientation of the axis of that cylindrical
lens. Toric lenses are used in optical
aids. They are also used in certain types of implants to
correct for astigmatic refractive
errors most often in combination with a spherical lens
(see sphere above) to correct for the spherical error (e.g. a
toric phakic IOL see above and also see our PDF files on
intra-ocular lenses).
Trabecular meshwork
This is the term for that specialised area of tissue
which is situated in the drainage
angle of the eye and through which the aqueous humour
leaves the eye and subsequently gains access to the venous
system. Resistance to the outflow of this fluid results in an
increase in the intra-ocular
pressure. Persistent elevation of the IOP in primary open
angle Glaucoma
results in damage to the visual fields and if untreated can
result in blindness. It is towards this particular tissue that
laser treatments to lower the IOP are directed. In previous
years a thermal laser was used in argon laser trabeculoplasty
(i.e. ALT) in an attempt to open up the spaces between the
delicate fibres of the trabecular
meshwork. By opening up these spaces the treatment was
designed to increase the facility for the aqueous to leave the
eye and hence to lower IOP. There is now a less invasive and
destructive laser treatment available in which gentle laser
energy is applied to the trabecular tissue. This results in a
biological effect that results in a lowering of the IOP
without any long term damage to the trabecular
meshwork. This treatment, which is known as selective
laser trabeculoplasty, has been shown to be effective in
lowering IOP. This means that it may be used in conjunction
with or occasionally instead of topical IOP lowering agents.
If the IOP cannot be controlled with laser or topical
drops, either alone or in combination, then Glaucoma
drainage surgery may be required to do so. In the most modern
types of such operations part of the trabecular
meshwork tissue may be removed in the course of the
operation (e.g. in deep sclerostomy procedures).
Trabeculectomy
This is the
name for the standard and very effective operation to treat
uncontrolled IOP in Glaucoma
(see above). This operation is classified as a penetrating Glaucoma
operation due to the fact that a tiny full thickness opening
in the sclera
(which is known as a sclerostomy) is made to allow drainage of
the aqueous humour into the sub-conjunctival space. This
results in a continuous controlled drainage of the aqueous
with consequent lowering of the IOP. There are also now many
variations of effective non-penetrating Glaucoma
operations that are also used to lower IOP in a controlled
manner. These use very deep scleral dissections (which are
known as sclerotomies) in a combination with either injection
of visco-elastic material or else cannulation of the Schlemm's
canal. In some variations of these operations an implant may
be placed into a deep sclerostomy and be covered over by a
combination of a scleral flap and conjunctiva.
The aqueous then egresses form the eye through the very thin
remaining sclera
to gain access to the Schlemm's canal. trabecular
meshwork tissue can also be removed in such operations in
the area of the sclerostomy.
Tracking system
This is the
term for the system on the excimer
laser that allows the laser to remain correctly aligned
with the eye throughout the course of a laser corrective eye
surgery procedure. It uses a software system that recognises
iris
landmarks and samples the position of the up to 200 times per
second. At the Ardfallen Eye Clinic the Technolas
excimer
laser that we use to perform our excimer
laser treatments has a 200Hz tracker. This allows for
highly complex Wavefront
designed customised
ablations designed by our surgeon using his own
personalised nomogram in conjunction with the Zyoptix treatment calculator to be safely and effectively used in treating our laser
corrective eye surgery patients.
Transition zone
This is the
term for the area where the ablation in an excimer
laser corrective eye surgery procedure blends into the
normal non-ablated cornea.
When the optical zone and the transition zone are correctly
designed in any individual it decreases the possibility of any
glare
and haloes occurring after excimer
laser treatments. The pupil
measurements captured by the pupilometer during the optical
work-up are used in the design of the dimensions of the
optical zone and transitions zone along with other data (such
as the corneal thickness and refractive
error being treated).
Trauma
Trauma can affect the eye in
many different ways. For example blunt trauma may result in a
small haemorrhage into the anterior chamber which results in
an inferiorly located collection of blood which is known as a
hyphaema. It may also result in damage to the zonules
with a partial or in some cases complete dislocation of the crystalline
lens. If a patient who has previously had any form of
ophthalmic surgery sustains trauma to their eye then they
should be examined by their ophthalmic surgeon as soon as
possible. If there is any damage that requires treatment then
it is best that this is detected at the earliest possible
stage. Similarly if a person is presenting for any form of
ophthalmic surgery who has previously sustained any
significant trauma to either eye then they should alert their
ophthalmologist to this fact as it may have a major bearing on
any potential treatment that is being contemplated.
Twenty-twenty
This is the
common term for the visual
acuity in a normal sighted person measured with a Snellen
chart (see above).
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U
Uncorrected visual acuity (UCVA)
This
is the term for the visual acuity without the assistance of
any optical
aids. It is synonymous with the terms unaided acuity or
unaided vision which generally refer to the level of vision
achieved after corrective eye surgery without the assistance
of any optical
aids.
Under-correction
This term
refers to where there is less of a correction of the refractive
error that was being treated. This can easily be corrected
with an enhancement procedure after a period of stabilisation.
In certain patients an under-correction may actually be the
intended refractive target (see above).
Uvea
The uvea (or uveal tract as it is
also known) consists of the iris,
the ciliary body and the choroid
from front to back.
Uveitis
This is the term for an inflammation
of the uvea
or uveal tract (see above). It may affect either the entire
tract (when it is then known as a panuveitis) or else just the
anterior portion (when it is known as an iritis or else an
irido-cyclitis) or else the posterior portion of the tract
(when it is known as a choroiditis). Most commonly uveitis
occurs as an idiopathic condition (i.e. it affects only the
eye and there is no associated systemic disease) but it also
occurs as part of a systemic condition.
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V
Vaccinations
If a prospective
candidate is contemplating a foreign trip that requires
vaccination against potential tropical infections then they
should arrange to have the required vaccinations administered
at least a week prior to their being treated with excimer
laser corrective eye surgery. It would also be appropriate
to wait at least that length of time after the treatment prior
to having vaccinations. These injections can occasionally
react with other medications that may require to be used
before or after excimer
laser treatment.
Varifocals
This is the term for
glasses that are graduated for the power of the lens from the
top down with the weakest power for distance viewing being in
that part of the lens that is looked through when looking
straight ahead. As the line of vision moves downwards, when
viewing objects closer, the power of the lens gradually
increases until the maximum power in present in the lower part
of the lens where the reading correction is incorporated. This
therefore allows clear vision at all viewing distances. This
type of spectacle lens is only required for people who are presbyopic.
Some people find wearing varifocals easy and some people can
never easily adapt to them.
Vertigo
This is the medical term
for dizziness. It can be an occasional transient symptom after
any refractive
surgery procedure. It generally subsides fairly quickly
after a period of neural
adaptation. This type of symptom is most commonly seen
after one eye has been treated (e.g. with an implant
technique) and it occurs in the time interval between the
first eye and the second eye being treated. At the Ardfallen
Eye Clinic we always strive to treat the two eyes together
when it is possible to perform a lasik
correction to minimise this problem for our patients. We also
strive to shorten in as much as is safely possible the time
interval between treating the second eye when it is necessary
to treat the two eyes separately (as with an implant
technique).
Visco-elastics
These are
solutions that are used in ophthalmic surgery to maintain the
volume of the eye during intra-ocular surgery. They are
specially designed to be safe to use within the eye and assist
in making the surgical procedures easier to perform. At the
end of the surgery they are removed from the eye and the
aqueous then fills up the anterior chamber again.
Visual axis
This is the line of
sight (i.e. the principal axis along which the light travels
through the focusing mechanism of the eye to the fovea
in the centre of the macula).
Visual
acuity
This is the term that describes the measurement
of how well we see in terms of the sharpness of our vision
(see acuity above for a fuller explanation).
Visual fields
The visual field
is the area in space that each eye perceives images. The
visual field may be damaged in a number of conditions (e.g.
see Glaucoma
above). At the Ardfallen Eye Clinic we have our own visual
fields analyser. We use the Zeiss Humphrey visual fields
analyser which is the recognised "gold standard" visual field
analyser that is used in peer review journals in publishing Glaucoma
studies. This machine can test both the central and the
peripheral monocular fields as well as the binocular
functional fields.
Visual potential
This term
is used to describe the best possible visual
acuity that could be expected to be achieved with any form
of surgical procedure in any individual eye. It can be
estimated using a variety of techniques. The pinhole is the
most commonly used device to assess this in the clinical
setting.
Visual
requirements
This term refers to the level of visual
acuity that is a minimum standard required for any
individual to take up employment in the particular occupation
in question (see occupation above for links to the web sites
for various different occupations where their particular
visual requirements will be available for perusal).
Vitrectomy
This is the name for
an operation in which the vitreous
gel is removed from the eye and replaced with an infusion
initially which then becomes replaced by the aqueous over
time. An anterior skirt of vitreous
gel is left after the surgery attached to the vitreous
base (see below). A vitrectomy is performed by making three
small sclerotomies. An infusion is secured in one of these
while a cutting instrument (which is known as a vitrector) and
a small light pipe are alternately passed through the other
two sclerotomies. The light pipe provides internal
illumination of the vitreous cavity and retina
while the vitrector cuts the vitreous into tiny portions which
are then aspirated out of the eye. As three ports are used to
perform this operation and as they are located in the pars
plana (see vitreous base below) the operation is frequently
referred to a trans pars plana vitrectomy (or TPPV). TPPV is
used in retinal detachment operations and also to remove the
vitreous if it has become cloudy (e.g. due to an internal
ocular haemorrhage in advanced diabetic eye disease - see
diabetes and diabetic eye disease above) or fibrosed (as for
example after severe ocular trauma).
Vitreous base
This is the name
for the area in the eye where the anterior attachment of the
vitreous
gel is located. It straddles the most anterior portion of
the retina
and the most posterior portion of the ciliary body (which is
known as the pars plana).
Vitreous gel (or
humour)
This is the term for the normally clear
colourless gel that fills the biggest space in the eye (i.e.
the vitreous cavity). The vitreous cavity is located between
the back of the lens and its zonules
and in front of the retina.
The vitreous can only undergo a limited repertoire of change
in life. It generally remains clear but it can split into more
solid and liquid components and these may cast a shadow on the
retina
and be perceived as a floater within the eye. Occasionally the
vitreous loses volume later in life and it may then detach
itself form its normal attachment around the optic nerve head
to form a posterior vitreous detachment (see our Eye Motion
education centre for more information).
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W
Watery eyes
This refers to a
situation where the eyes water excessively. The medical term
for a watering eye is epiphora. The eyes may water for one of
two reasons. Firstly they may water due to an infection,
allergy or else an inflammation.
Alternatively they may water because of an obstruction to the
drainage of the tears through the lacrimal system (see above
for more information).
Wavefront
This term describes the
concept of measuring the higher
order aberrations of every eye and then using this
information to design a customised
ablation for that eye. This information is then programmed
into the Zyoptix treatment calculator software and our surgeon then uses his own
personalised nomogram
to personally design a customised
ablation for each individual eye being treated. This so
called "shot
file" is then programmed into the excimer
laser and the eye has its refractive
error corrected to provide the best quality visual result.
All our patients at the Ardfallen Eye Clinic have a Wavefront
correction when their refractive
error is being treated (see higher
order aberrations above for further information). If a
patient is considering undergoing refractive
surgery at any centre then they should ensure that they
will receive a Wavefront designed customised
ablation and that the surgeon designing it has experience
in this area. They should also question as to what system is
being used to derive the measurements required to design the
treatment. If the answers to these questions are not
satisfactory then it is likely that they will not be receiving
the best quality and most modern treatment available with the
current technology available. A treatment that is based on
measurements made by an optometrist with no personalised input
from an experienced refractive surgeon is definitely not of
the same standard as one that has an experienced surgeon's own
personal input.
Wavefront
aberrometer
This is the instrument that is used to
measure the higher
order aberrations in every eye to yield the information
that is required to design a customised
ablation for every eye. At the Ardfallen Eye Clinic we use
the Zywave aberrometer in conjunction with the Orbscan to measure the higher
order aberrations. This information is then programmed
into the Zyoptix treatment calculator software and our surgeon then combines this with his
own personalised nomogram
to design a shot
file for that particular eye (see Wavefront
and higher
order aberrations above). Anyone who is considering having
their refractive
error treated at any centre should ensure that they are
going to receive a Wavefront
designed treatment otherwise they will not be treated with the
most effective and up to-date technology available. They
should specifically ask if they are going to be treated with a
Wavefront
designed customised
ablation, what instrument is being used to capture the
data required to design such an ablation and what is the
surgeon's experience with this technology on the particular
type of excimer
laser that will be used to treat them. At the Ardfallen
Eye Clinic all our patients are treated with a Wavefront
designed customised
ablation which has been designed by our surgeon using his
own personalised nomogram.
He has treated successfully very many patients with this
technology (see our testimonial section for excimer
laser corrective eye surgery patient testimonials).
Weiss ring
This term
is used to describe the area of the cortex of the vitreous
gel that was previously firmly attached around the optic
nerve head prior to the development of a posterior vitreous
detachment (see PVD above and also see our Eye Motion section
for a dynamic depiction of a PVD). Following the development
of a posterior vitreous detachment the Weiss ring is perceived
as a floater in the patient's eye (see floaters above).
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Z
Zernike
polynomials
These are a set of complex mathematical
equations that are used to describe or classify the shape of
surfaces. In ophthalmology these are used in describing the higher
order aberrations of the optical system of the eye (see higher
order aberrations above for more information).
Zonules or zonular apparatus
The
zonules are the very fine strands that are attached to the
ciliary body at one end and the peripheral crystalline
lens capsule at the other end. They are responsible for
the stability of the crystalline
lens and in conditions where they are deficient (e.g. in
pseudo-exfoliation syndrome) or are damaged (e.g. post
significant ocular blunt trauma) then the support of the crystalline
lens becomes suspect. This can be seen on examination with
the slit lamp where the lens is seen to move with small ocular
movements (this is known as phaco-donesis).
Zyoptic treatment calculator
This is the software package that is used to design shot files for eyes that are to be treated with the Technolas excimer laser system that is manufactured by Bausch & Lomb. The data set that is used to do this is derived from measurements taken with the Zywave aberrometer in conjunction with measurements taken with the Orbscan.
Zywave
This is the aberrometer that is used to measure the higher order aberrations of eyes that are to be treated with the Technolas excimer laser system. The machine works by directing a beam of laser light on to the patient's retina for approximately 0.1 seconds. The light that is reflected from the focal point on the retina passes through the optical system of the eye and it is then directed through an array of lenslets (i.e. small lenses) in the body of the aberrometer. The beams, which are focused by the lenslet array, are arranged in a grid-like pattern which is known as a centroid pattern. The position of each of the points of light is detected by the Zywave aberrometer. The aberration of this Wavefront is then reconstructed from the distance of the individual points from what would be their optimal position if the eye being measured had no higher order aberrations.
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Ardfallen Eye Clinic, Suite1 Ardfallen Mall, Douglas Road, Cork
Tel: +35321 4291705 :: Fax: +353 21 4291724 :: E-mail: contact@eyelasercork.ie
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