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 Nidek OPD scan.
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.
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
Nidek laser system that is used by Ardfallen Eye Clinic is fitted with a 200Hz tracker which is 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
OPD scan) 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
OPD scan combined with the refractive data derived from the initial
consultation and the optical work-up. This information is then programmed into the
Final Fit 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.
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.
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
Nidek laser which is a scanning slit beam laser.
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.
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).
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
Nidek OPD scan. These are then manipulated with
Final Fit software provided by
Nidek 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.
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