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Glossary of Laser Eye Surgery Terms

Laser Eye Surgery Terms Beginning with 'A'
Aberrometer
A diagnostic device that measures the way light waves travel through the eye and any distortion the eyes optical system creates as the light passes through. Used in laser eye surgery to calculate wavefront guided treatments.
Ablation
The removal of tissue using an excimer laser in laser eye surgery to correct a refractive error. Used in LASIK and Epi-LASIK and the treatment of Keratoconus at AccuVision.
Accommodation
In optics this means the capability of the eye to automatically focus from distance to near objects and from near to distance objects.
Accommodation disorder
Where the eyes ability to focus from distance to near ojects and from near to distance does not work correctly. Disorders can be caused by a number of symptoms such as: eye strain, headache, difficulty concentrating (especially reading), blurred vision, double vision. Presbyopia is an example of an Accomodation disorder where near vision is impaired because the lens inside the eye can no longer focus the eye on near objects.
Age Related Macular Degeneration (AMD or ARMD)
Age Related Macular Degeneration is caused by damage to the retinal cones (the part of the eye that transfers images and colour to the brain). A gradual loss of central vision occurs leaving just the peripheral vision for seeing.
Allergy
The body's immune system is programmed to protect the body from foreign bodies e.g. pollen. Allergy symptoms can also affect the eyes, usually showing as redness of the eyes, tears, swollen eyelids or itching.
Amaurosis Fugax
This is sometimes described as an 'Eye Stroke'. It is caused when a blood clot restricts blood flow to the eyes causing temporary vision loss. It usually affects just one eye.
Amblyopia
Also known as Lazy Eye. If the central vision in one eye is less developed than the other, the brain becomes dependent on the information from the good dominant eye. An eye patch is used to help correct Amblyopia at an early age. The two main causes of lazy eye are Strabismus and Anisometroia. It can also be treated in adults using Neurovision.
Aniridia
A condition where the iris in the eye is either absent or partially absent. It is usually a congential defect in the eye and causes photophobia and poor vision.
Anisocoria
A condition where pupils are of unequal size. Causes are various including: a natural event in the population without a known cause, head or eye trauma, previous intraocular surgery, an infection of the membranes around the brain, an intercranial tumor and glaucoma.
Anisometropia
A common condition in people with impaired vision where the prescription needed for good vision is very different for each eye due to the differences in refractive power.
Anterior chamber
The part of the eye located behind the cornea and in front of the iris and lens.
Antibody
This is a specific protien that is initiated by the body's immune system to help fight foreign substances, toxins and infections inside the body.
Antioxidant
A substance that restricts oxidation thereby guarding persons from the effects of 'free radicals'. Free radicals are molecules with one or more unpaired electrons and they can destroy cells and can be part of the cause of various diseases. Antioxidant vitamins include vitamins B, C and beta carotene. Antioxidants may help prevent macular degeneration and eye diseases.
Aqueous humor
This is the clear fluid filling the front of the eye, located between the cornea and the iris. It supplies nutrients to the cornea and the lens. The fluid is created by the ciliary body. If this fluid is not able to drain away freely, pressure builds up and can cause Glaucoma. If this is not overcome, damage to the optic nerve can occur resulting in loss of vision.
Arcus
This describes fatty/oily deposits causing an opaque ring around the periphery of the cornea. It is a condition of elderly people but can also occur in people under the age of forty and is an indication of excessive level of cholesterol in the blood stream.
Aspheric
Meaning not quite a spherical shape. In vision terms people who suffer high perscriptions usually prefer aspheric glasses as they can be produced using thin lenses and lightweight frames and reduce eye magnification. Aspheric contact lenses are designed to overcome astigmatism and can also be used as a multi-focal lens.
Astigmatic Keratotomy
A surgical procedure involving the cutting of the cornea to facilitate making it more spherical after it has healed and thereby reducing astigmatism.
Astigmatism
Where the curvature of the cornea has developed in an asymmetrical shape (shaped like a rugby ball instead of a football). Consequently light entering the eye is focussed on two points on the retina rather than just one, which causes blurred vision. Astigmatism also causes double vision, squinting, eyestrain, distorted vision and shadowing around letters.
Atopy
Used to describe an increase in the antibody immunoglobin E that leads to conditions such as asthma, hay fever, eczema and rhinitis.
Laser Eye Surgery Terms Beginning with 'B'
Band keratopathy
Used to describe a loss of opacity in the corneal stroma and Bowman's membrane. It causes vision loss.
Best corrected visual acuity (BCVA)
This describes the best vision you can achieve using corrective glasses. It is a measure taken from the standard Snellen eye table. If you have bad eyesight with an uncorrrected reading of 20/300 but you are capable of seeing 20/20 using glasses then your Best corrected visual acuity is 20/20.
Bifocal
Where a lens is created with two focussing areas; one for close vision and one for distance vision. Lenses like this can be created for both glasses and contact lenses.
Binocular vision
The ability to focus on an object using two eyes simultaneously, thereby providing depth perception and clear focus.
Biocompatible
A material that is able to be placed inside the body or organs and not cause any adverse reaction. Intra Ocular lenses for example are boicompatible as they can be inserted inside the eye without any reaction from the body.
Blepharitis
An inflammation of the eyelid(s), usually around the eyelashes. Blepharitis can be caused by a number of conditions including: rosacea, dermatitis and allergies. The usual symptoms are a pink or red, sore looking eyelid, eyelid pain, swelling or crustiness.
Blepharoconjunctivitis
In addition to inflammation of the eyelid, the conjunctivitis also causes swelling with infection, tearing, burning around the eyes and severe discomfort.
Bowman's membrane
This is the corneal layer found between the epithelium and the stroma.
Laser Eye Surgery Terms Beginning with 'C'
Canaliculi
Very small channels found at the start of the tear ducts through which tears drain until they pass out into the nose.
Canaliculitis
An inflammation of a tear duct, usually caused by a bacterial infection. Symptoms for canaliculitis include a pink or red swollen eye, discharge from the eye and swollen eyelids close to the nose.
Capsulotomy
During cataract surgery the surgeon makes an incision into the capsule that holds the natural crystalline lens of the eye (a capsulotomy), which allows for the natual lens to be removed and substituted for an artificial intra ocular lens.
Cataract
A clouding over of the eyes' natural lens, the most common cause being age. Other causes are high exposure to the sun's ultra violet light. Smoking is also an identified cause. The symptoms are varied but can include: blurred vision, halos, glare around lights, cloudiness of vision and dimness of colour.
Cellulitis
An inflammation around the eye. There are a number of types. Orbital cellulitis affects the areas around the eyeball causing a bulging eye which should be dealt with immediately, while Pre-septal cellulitis affects the eye lid and other parts around the eye, causing swollen eyelids and discomfort around the eyes.
Central island
Used to describe a refractive laser eye surgery complication where a small area of cornal tissue is left untreated in the ablation zone. This can cause double vision and sight distortion.
Chemosis
A swelling on the conjunctiva that is usually caused by an allergy.
Choroid
The fine layers of blood vessels that are situated between the white of the eyes (sclera) and the retina. Their function is to maintain a supply of nourishment to the back to the eye.
Ciliary body
The ciliary body holds the natural lens inside the eye in place and also causes it to change shape so that fine focussing is possible (accomodation). It also produces aqueous humor.
Collagen
Fibrous protein present in the eye that makes up the structure of the cornea clear at the front of the eye.
Colour blindness
The inability to distinguish specific colours from the colour spectrum. Colour blindness is an inherited condition and is prevalent in men more than women.
Computer vision syndrome
Symptoms of computer vision syndrome include headaches, shoulder and neck pain, eyestrain, dry eyes, blurred vision, pink or red eyes or even light sensitivity. It is important to get an assessment for these conditions as the symptoms are also common to other conditions.
Concentric
Having a common center; extending out equally in all directions from a common center.
Conductive Keratoplasty
Procedure in which a surgeon applies radio waves to the cornea to heat the collagen in the cornea's periphery. This causes it to shrink, thereby reducing hyperopia.
Cone
Found in the retina. A cone is a photosensitive receptor that helps a person differentiate colours and there are approximately 6,400,000 in the human retina.
Conjunctiva
The conjunctiva is a thin clear membrane that overlays the inner surface of the eyelid and the white part of the eyeball (the sclera).
Conjunctivitis
This is an inflammation of the conjunctiva, which causes redness of the eye and discharge from the eye. A burning sensation and itching can occur along with light sensitivity and eye pain. It can occur in one or both eyes.
Contact lens
A transparent material that is usually placed on the surface of the eye (cornea) that is designed to help refract light through the eye and onto the retina in the correct way.
Contact lens problems
Contact lens problems can occur and they can range from minor irritations to sight impairment, and include protein build-up, dirt, dust or debris on the lens, a damaged lens, infections caused by incorrect lens cleaning procedures. Symptoms of contact lens problems can involve rapid blinking, blurriness of vision, burning sensations in the eye, discharge of fluid, foreign body sensation in the eye, itchiness, sensitivity to light, pain in the eye, pink eye or red eye or swelling of the eylid.
Contact lens solution
Used by contact lens wearers to help with the comfort of wearing contact lenses.
Contrast sensitivity
The ability of the eye to perceive differences between an object and its background, i.e. the ability to identify a blue object on a blue background.
Convergence
Where a person's eyes begin to turn inwards. Performing close up tasks like reading may cause eye strain and blurred vision.
Cornea
The transparent front part of the external structure of the eye covering the iris, the pupil and the sclera. The dome-like shape of the cornea delivers approximately two-thirds of the optical power of the eye. Light passes into the eye through the cornea. It is reflected back out of the eye, making the iris and pupil of the eye visible.
Corneal abrasion
Usually caused by contact lens wear or a sports injury or dirt or other foreign body infecting the eye. Blurred vision, grittiness, eye pain and light sensitivity.
Corneal dystrophy
A condition where the clear window at the front of the eye (the cornea) loses its transparency. The surface of the cornea is no longer smooth which causes blurred vision, light sensitivity, eye pain and vision loss.
Corneal edema
A swelling of the cornea that can be as a result of intra ocular surgery, high intra ocular pressure, contact lens problems, or other corneal dystrophies. Symptoms can include halos around bright lights, eye pain, foreign body sensation or vision loss.
Corneal erosion
Continuing breakdown of the corneal epithelium. Symptoms include blurred vision, foreign body sensation and eye pain or discomfort.
Corneal implants
Vision correcting elements like corneal rings or contacts that are placed inside the eye structure to correct vision.
Corneal opacity
Where a translucent or small cloudy area is found in the cornea caused by scarring or an infection. Sufferers can experience halos around lights, vision loss and a visible cloudy spot on the eye.
Corneal ring
These are used in corrective surgery. A surgeon inserts a clear plastic ring into the cornea which then reshapes it to help with focussing the light entering the eye on to the retina.
Corneal topography
This is measured using a corneal topographer which directs light onto the surface of the eye and then is able to accurately measure the light as it is reflected back into the device so that a detailed corneal map can be created showing it's curvature and any irregularities it may contain in its structure. The corneal topographer produces a coloured map that clearly shows the variations in shape and height of the cornea. Very good for consulting on astigmatism, laser eye surgery and specialist contact lens fitting.
Crossed eyes
This condition is where both eyes are misaligned and pointing inwards. It is a type of strabismus.
Cystoid macular edema
This condition describes when the eyes macula can be affected by an excessive amount of fluid in the eye and cause the macula to swell.
Cytomegalovirus retinitis (CMV retinitis)
An eye infection associated with immune deficiency such as AIDS. Major symptoms include blind spots blurred vision, vision loss and floaters.
Laser Eye Surgery Terms Beginning with 'D'
Dacryoadenitis
This condition describes the inflammation of the tear gland. The cause is usually a viral or bacterial infection. The resulting symptoms include red eyelids or swelling around the eyes.
Dacryocystitis
Condition caused by the swelling or inflammation of the nasolacrimal or tear sac. Symptoms can include sticky eyes, eye discomfort and tearing.
Dacryostenosis
This condition is where the tear duct becomes blocked, causing tears and some discharge.
Descemet's membrane
This is found in the cornea and is found between the stroma and the endothelium.
Diabetic maculopathy
A disease of the eye that occurs in diabetics. It causes swelling in the eye, and discharge of fluids and disolved fats into the macula. It can cause loss of vision and blindness.
Diabetic retinopathy
A condition affecting long term diabetes sufferers. Retinal blood vessels begin to discharge which affects the functioning of the macula. Blurred vision may be the first symptom or a larger number of floaters but can progress to loss of vision.
Diabetic vitreous hemorrhage
Caused by weakening of blood vessels in the eye, the bleeding into the vitreous humor obscures clear vision and may require surgery.
Diopter
Used as a measure for refraction or bending of light through a substance. Opticians use diopter measurements to describe prescriptions for contact lenses and spectacles to provide clear vision for patients. A positive number would describe a long-sightedness condition and would be written as +3.00D for instance. A negative number would describe a short-sightedness prescription and would be written as -7.25D.
Diplopia
Diplopia is used to describe double vision. This occurs when one or both eyes percieve two images at the same time.
Disc hemorrhage
The optic disc at the back of the eye is where the optic nerve is attached to the back of the retina. Bleeding around the edge of the disc can occur and is one indication of glaucoma.
Disposable contact lenses
Some contact lenses are now produed so that they can be thrown away after a short period of wear. This time period can range from just a day to a couple of weeks.
Dk/t
Used to describe the permeability and thickness of a contact lens. The Dk value is the oxygen permeability of the contact lens material. The t value indicates its thickness which affects the transfer of oxygen through the contact lens.
Double vision
Also referrred to as diplopia. See diplopia.
Drainage angle
In reference to glaucoma a drainage angle relates to the drainage channel for the aqueous humor in the front part of the eye. Reduced drainage can naturally lead to higher intraocular pressure which is linked to glaucoma. Open angle glaucoma occurs when the body produces too much fluid for the eyes whereas narrow angle glaucoma occurs when the drainage channel is blocked.
Druse
Describes a deposit in the eye that can be white or yellow. Druse is sometimes linked to macular degeneration.
Dry eye
Occurs when the body in unable to produce enough lubrication and moisture for the eye. This is usually a temporary condition.
Dry eye syndrome
Dry eye can occur through aging or long term contact lens wear. It can also be part of a number of systemic diseases. Dry eye syndrome can cause eye pain, a burning sensation in the eyes, itching and frequent blinking.
Laser Eye Surgery Terms Beginning with 'E'
Emmetropia
This describes the condition of an eye with normal vision where light is correctly focused on the right part of the retina at the back of the eye.
Enophthalmos
The recession of an eyeball into the orbit. Causes include developmental problems, trauma and inflammation.
Entropion
An abnormal inward turning of an eyelid (usually the lower lid), which causes the lashes to rub on the ocular surface; usually due to aging. Additional symptoms include eye or lid pain or discomfort, redness, itching, tearing and vision loss if there is damage to the cornea.
Epiretinal membrane
Thin layer of scar tissue on the retina which forms as a result of changes in the vitreous gel. Also called a macular pucker. In its early stages, an epiretinal membrane is often asymptomatic, but some people have blurred vision. There may be symptoms of distortion or metamorphopsia.
Episclera
The outermost layer of the eye's sclera that loosely connects it to the conjunctiva.
Episcleritis
Inflammation of the episclera. The cause is usually unknown, but episcleritis may be associated with some systemic (e.g. autoimmune) diseases. Symptoms include a red eye, pain or discomfort, light sensitivity and tearing.
Epithelial in-growth
A LASIK complication in which epithelial cells migrate and grow under the LASIK flap; epithelial ingrowth does not usually affect vision. Reported incidence is low (0,1%).
Epithelium
The cornea's outer layer of cells. The only layer of the cornea that has the ability to replicate if damaged.
Esotropia
A form of 'squint' or strabismus where one or both eyes point inward, so the eyes are "crossed." Commonly erroneously referred to as 'lazy eye'. Management options include glasses, orthoptic exercises or surgery.
Excimer laser
An instrument that uses ultraviolet wavelength of light to vaporize and remove tissue from the eye's surface during vision correction procedures. Rather than burning or cutting material, the excimer laser adds enough energy to disrupt the molecular bonds of the surface tissue, which effectively disintegrates into the air in a tightly controlled manner through ablation rather than burning.
Exotropia
A form of 'squint' or strabismus where one or both eyes point outward. Management includes orthoptic exercises or surgery.
Extended wear
Currently, these contact lenses are approved to be worn without removal from 1 week to 1 month, meaning some people will be comfortable sleeping with them in their eyes. Sometimes referred to as continuous wear. Known risks include corneal infection.
Eye tumor
An abnormal growth or mass that occurs in or next to the eye. Tumors can be both benign and malignant and primary or secondary (from other organs). They include the dermoid cyst, capillary hemangioma, cavernous hemangioma, choroidal melanoma, retinoblastoma and lymphoma. Symptoms can include blurred vision, a bulging eye, double vision, floaters, foreign body sensation, pain or discomfort in the eye, the lid or around the eye, swelling of the lid or around the eye, a red or pink eye, ptosis, vision loss, limited eye or lid movement, a white or cloudy spot on the eye, and an iris defect. Various treatment options exists depending on the type of tumor.
Laser Eye Surgery Terms Beginning with 'F'
Far-sightedness
Also called hyperopia. Occurs when the length of the eye is too short or the optical power of the cornea and lens too low. To far-sighted people, near objects are blurry, but far objects are in focus.
Femtosecond laser
A laser device that creates bursts of laser energy at an extremely fast rate measured in terms of a unit known as a femtosecond (one quadrillionth of a second). These ultra fast energy pulses precisely target and break apart tissue or other substances at a molecular level, without damaging adjacent areas. Commonly used in corneal refractive surgery e.g. to create LASIK flaps.
Fixation
The eye's ability to maintain gaze upon an object or target.
Floaters
Floaters are very common and may look like clouds, strands, webs, spots, squiggles, wavy lines or other shapes and often move in the field of vision. As the eye ages, the gelatinous vitreous humor begins to liquefy in the center of the gel. Floaters are caused by the undissolved vitreous humor that floats in the liquid vitreous. Sometimes, a "shower of floaters" is a sign of a serious condition, particularly if you also see flashes of light. Floaters are more commonly seen in short-sighted eyes.
Fluorescein
A staining agent that becomes a bright, fluorescent yellow-green when in contact with alkaline substances. A fluorescein dye solution is routinely used by optometrists and ophthalmologists as a diagnostic agent in contact lens fitting and assessment of corneal lesions or to conduct tests for eye dryness used with a blue filtered light.
Fluorescein angiography
An imaging test that involves injecting fluorescent yellow-green dye into the veins. When the dye reaches interior regions of the eye, it provides opportunity for high contrast photography or other imaging of blood vessels. This is particularly useful in diagnosing conditions such as age-related macular degeneration, which in advanced forms can be characterized by abnormal growth of blood vessels in the retina.
Foreign body
A foreign object or particle found in the eye. Symptoms include foreign gritty irritation, eye pain or discomfort, a red or pink eye, tearing, frequent blinking, blurred vision, discharge, light sensitivity and vision loss.
Fovea
A depression in the retina that contains only cones (not rods), and that provides acute eyesight. Ideally the area of the retina where light is focused to form an image.
Frequent replacement contact lenses
Also called planned replacement. Technically, this is any contact lens that is thrown away after a moderately short period of time. Among most eye care practitioners, "disposable" usage ranges from one day to two weeks, while "frequent replacement" lenses are discarded monthly or quarterly.
Laser Eye Surgery Terms Beginning with 'G'
Glaucoma
An eye disorder in which the optic nerve suffers damage, permanently impacting vision in the affected eye(s) starting with peripheral vision loss and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye. Glaucoma can be divided roughly into two main categories, "open angle" and "closed angle" glaucoma. Closed angle glaucoma can appear suddenly and is often painful; visual loss can progress quickly but the discomfort often leads patients to seek medical attention before permanent damage occurs. Open angle, chronic glaucoma tends to progress at a slower rate and the patient may not notice that they have lost vision until the disease has progressed significantly.
Graves' disease
An eye disorder associated with abnormalities of the thyroid gland; symptoms include eyelid retraction, bulging eyes, light sensitivity, eye discomfort, double vision, vision loss, a red or pink eye and a limited ability to move the eyes.
Laser Eye Surgery Terms Beginning with 'H'
Hard contact lenses
Rarely worn now, hard lenses are made of PMMA material. Cannot transmit oxygen through the lens to the cornea and often cause warpage of the cornea's shape. Compared with modern soft and rigid lenses, they are less healthy to wear long-term.
Herpes eye infection
Typically causes infection in the corneal stroma with characteristic dendrite shaped lesions. Symptoms include pain, redness and reduced vision. The virus stays dormant and infection can be triggered by ill health or trauma.
Heterochromia
Condition where one iris of an eye is a different colour to the other, or where one eye is more than one colour.
High-index
Type of lens with a higher index of refraction, meaning that light travels faster through the lens to reach the eye than with traditional glass or plastic. It is denser, so the same amount of optical correction occurs with less material - so the lens can be thinner.
Higher-order aberration
Higher-order aberrations are visual problems that cannot be diagnosed using a traditional eye exam, which tests only for acuteness of vision. Severe aberrations can cause significant vision impairment. These aberrations include starbursts, ghosting, halos, double vision and contrast loss. They are optical errors of the eye other than a refractive error (myopia, hyperopia or astigmatism) and cannot be corrected by traditional eye glasses.
Histamine
A protein that can be released as part of the body's immune system responses during an allergic reaction. Presence of histamine can lead to inflammation and swelling, which is why antihistamines often are prescribed for allergy symptoms.
Horner's syndrome
Condition characterized by a small pupil, ptosis (drooping upper eyelid) and an abnormal lack of facial perspiration (all on the same side of the face); Horner's syndrome is caused by injury to the sympathetic nerves of the face.
Hyperopia
Also called far-sightedness. Condition in which the length of the eye is too short, causing light rays to focus behind the retina rather than on it, resulting in blurred near vision. Additional symptoms include eyestrain and squinting. It is corrected by positive powered lenses.
Hypotony
Abnormally low intraocular pressure, often caused by eye surgery or trauma (e.g. open globe injury). Could indicate fluid leakage or deflation of the eyeball.
Laser Eye Surgery Terms Beginning with 'I'
Intraocular lenses (IOL)
An artificial lens that is implanted in the eye, generally after the eye's natural crystalline lens (see Lens, Crystalline) has been removed. IOL's are used on patients suffering from Cataracts or as an alternative to Laser Eye Surgery to correct large visual prescriptions.
Intraocular pressure (IOP)
The fluid pressure of aqueous humor. Measuring the IOP is important in detecting for and monitoring of Glaucoma.
Iris
A pigmented membrane that controls the diameter of the pupil according to ambient lighting conditions.
Iritis
Inflammation of the iris, a form of Anterior Uveitis. A number of causes and conditions are associated.
Laser Eye Surgery Terms Beginning with 'J'
We're sorry, but we haven't added any laser eye surgery terms beginning with the letter 'J' to the glossary.
Laser Eye Surgery Terms Beginning with 'K'
Keratectomy
Surgical removal of part of the cornea. See (PTK) Phototherapeutic Keratectomy.
Keratitis
An inflammation of the cornea, caused by an infection or inflammatory process. Causes can include any or a combination of the following : Bacterial, Amoebic, Viral, Fungal, Onchocercal, Exposure, PhotoUV (Snow Blindness, Arc eye), Ulcerative, Contact Lens wear and Severe allergic response. Untreated keratitis can lead to corneal scarring and associated loss of vision. Symptoms include eye pain or discomfort, light sensitivity, foreign body sensation, grittiness and tearing.
Keratoconjunctivitis
Inflammation of the cornea as well as the conjunctiva. The two commonest forms include Vernal Keratoconjunctivitis and Keratoconjunctivitis Sicca.
Keratoconjunctivitis (sicca)
More commonly referred to as dry eye syndrome. Normally due to a chronic lack of sufficient lubrication and moisture in the eye. Dry eyes are a common complaint amongst Contact Lens wearers.
Keratoconjunctivitis (vernal)
Seasonal inflammation of the conjunctiva. Also known as Warm Weather conjunctivitis or Spring Catarrh. Strong association with atopy (hayfever, asthma & eczema).
Keratoconus
A degenerative disorder of the cornea causing progressive thinning and conical curvature of the cornea leading to decreased vision. Kerataconus is the most common form of Corneal Ectasia. Without medical intervention, keratoconus often causes the perforation (Hydrops) of the cornea requiring a corneal transplant or graft. The exact cause or trigger mechanism is not known, however a strong autosomnal genetic link amongst environmental and cellular factors are indicated. LASIK refractive surgery has also induced keratoconus, see Post-LASIK Ectasia. Corneal Collagen Cross-linking is the only treatment shown to halt the progressive nature of the disorder.
Keratometer
An instrument that measures the curvature of the cornea. Keratometry is relevant to laser and IOL refractive surgery, keratoconus and contact lens fitting.
Keratoplasty
Any of several types of corneal transplantation or graft. These are either complete transplants (penetrating keratoplasty) or part grafts (lamellar keratoplasty).
Keratotomy
Incision of the cornea. Most commonly associated with Radial Keratotomy (RK).
Laser Eye Surgery Terms Beginning with 'L'
Lacrimal plug see Punctal plug
Made either of collagen (temporary) or silicone (permanent), punctual plugs are sometimes inserted into the puncta (tear duct) of the lower lid to stop tear drainage.
LASEK (Laser Epithelial Keratomileusis)
A popular laser refractive treatment. Commonly used on patients that are involved in contact activities or patients deemed ill suited to LASIK. The corneal epithelium is scraped off after exposure to a dilute (18%) alcohol solution. An excimer laser then ablates Bowman's membrane and the stroma to the desired correction. A contact lens is placed on the eye until such time as the epithelium has regenerated. Wound healing typically takes 4-5 days and visual recovery longer. Post-operative visual acuity matches that of LASIK between 2 and 3 weeks post treatment.
Laser photocoagulation
A procedure using a laser, normally to cauterise blood vessels on the retina. Most commonly used in providing therapeutic treatment for Diabetic Retinopathy and more recently age related macular degeneration.
LASIK (Laser-Assisted In Situ Keratomileusis)
The most popular form of elective refractive treatment. A corneal flap is cut using either a Microkeratome or Femtosecond laser. The flap is folded back before an excimer laser ablates the desired correction. The flap is folded back into position prior to completing treatment. Wound healing is quick, with the epithelium sealing within 24-48 hours. Visual recovery can take from as little as 24hrs up to 2 weeks in some cases. The treatment is popular due to the pain free recovery and quick visual rehabilitation.
Lens (crystalline)
A structure in the eye that along with the cornea focuses light on the retina. The lens unlike the cornea does this by changing shape. The shape change allows for a change in focal point (accommodation). As the lens ages (38-45 yrs), it starts to lose elasticity causing presbyopia (loss of near focusing). The lens can undergo opacification for a number of reasons, causing a Cataract.
Lens (optical)
Any optical device that transmits and refracts light.
Lens dislocation (Ectopia lentis)
Full or partial displacement of the eye's lens. Dislocation is commonly associated with a number of systematic syndromes as well as trauma.
Leukocoria
An abnormal (white) reflection of the eye. Commonly noted in photos taken with a flash (as opposed to the usual red reflection). While noted in a number of other conditions, Leukocoria is most prominently associated with the eye cancer retinoblastoma.
Limbal relaxing incisions
Are surgical incisions of the corneal edge or limbus, often performed during cataract surgery. As opposed to Radial Keratotomy (RK), these incisions are not particularly deep or near the visual field of the eye. These incision are typically made to correct for minor amount of corneal astigmatism.
Limbus
The border of the cornea and sclera.
Lupus (systematic lupus erythematosus)
Is a systematic auto-immune disease that causes inflammation and tissue destruction. Lupus is more prevalent in non-europeans and is found much more commonly in women. While Lupus is more noticeable on the dermus, it can have optical symptoms such as a red or pink lid, eyelash loss, dry eye syndrome, uveitis, scleritis, migraines, conjunctivitis and retinal vascular occlusion.
Laser Eye Surgery Terms Beginning with 'M'
Macula
A small area near the centre of the retina which has the greatest density of cone receptor cells necessary for good visual acuity and colour vision.
Macular degeneration
This condition causes a general deterioration in visual acuity progressing to loss of central vision due to changes in the macular tissue. It usually affects older adults. Research suggests that there may be links to high cholesterol, smoking or a genetic predisposition to the disorder.
Macular edema
This condition occurs when fluid leaking from retinal blood vessels causes the macula to become swollen. It causes temporary vision loss which may become permanent if untreated.
Macular hole
As we age the vitreous shrinks and this can cause a hole to develop in the macula. This in turn results in blurring, distortion or loss of central vision.
Maculopathy
Any deterioration of the macular tissue. Symptoms include blurring, distortion or loss of central vision.
Meibomian gland
Situated at the base of the eyelashes this gland secretes a lipid substance which constitutes part of the tear film.
Meibomianitis
This condition occurs when the meibomian glands become inflamed resulting in redness and swelling of the eye. In addition, vision may be blurred and there may be a burning sensation due to poor tear film.
Melanin
Naturally occurring pigment present in skin and hair as well as the iris of the eye thereby defining eye colour.
Melanosis
Deposits of melanin.
Meridian
The angles relative to the horizontal plane through the centre of the pupil at which the cylindrical powers needs to be set to correct astigmatism.
Metamorphopsia
Distortion of vision whereby straight lines may appear to be curved, objects may be magnified or minified, and depth perception may be impaired.
Microaneurysm
In the eye these present themselves as small red spots in the retina. They are one of the earliest signs of diabetic retinopathy. They occur as a result of damage to the walls of blood vessels due to high sugar level in the blood. Eventually they can lead to impaired blood supply to the retina which in turn cause damage to the eye that could cause loss of vision if untreated.
Microcornea
A cornea that is unusually small in diameter and has steep curvature.
Microkeratome
Semi-automated device with an oscillating blade which creates the flap of tissue on the front of the cornea in the LASIK procedure.
Microphthalmia
Abnormal development of the eye where the eye does not grow to its full size resulting in one or both eyes being abnormally small.
Migraine
A condition characterized by severe headaches which may be accompanied by nausea. In addition patients frequently experience visual disturbances including photophobia, blurred vision, halos round lights and blind spots or tunnel vision. Patients may experience the visual disturbances without developing a headache.
Minification
Concave lenses in spectacles to correct myopia cause objects to appear reduced resulting in minification.
Mixed astigmatism
Where the curvature of the two main meridians of the cornea differ so that one meridian is hyperopic and the other myopic. This results in blurred vision both distance and near.
Monochromatic
A source of light made up of one wavelength only.
Monofocal
A lens which has one focal length therefore it corrects vision to a single fixed distance.
Monovision
Refers to monofocal correction in each eye where the dominant eye is corrected for distance vision and the other eye is corrected to a shorter focal length for near vision. Monovision is often used for patients who have presbyopia to reduce the need for separate reading glasses.
Mucin
A glyco-protein which forms part of the tear film. It increases viscosity of the tear film necessary for effective lubrication of the eye.
Multifocal
Lenses which are designed to have a transition of varying power from the centre of the lens so that presbyopes focus at different distances through different parts of the same lens.
Myasthenia gravis
An auto-immune disease which causes voluntary muscles to weaken. Symptoms associated with the eye include diplopia and drooping of one or both eyelids.
Myopia
Medical term for short-sightedness. It occurs when the axial length of the eye is too long relative to the curvature of the cornea and the power of the lens within the eye. Distant images are focussed in front of the retina and therefore blurred.
Laser Eye Surgery Terms Beginning with 'N'
Naevus
A dark lesion with defined outline often called a birthmark or mole. They may be found on the skin as well as in the eye. Generally these lesions are benign but they should be monitored over time in case they change into a melanoma which is a form of cancer.
Nanometer
A unit of measure used to define wavelength of different types of light.
Near-sightedness
Another term for myopia (see definition).
Neovascularization
Formation of micro-vascular network of new blood vessels from pre-existing ones. It can be associated with over-wear of contact lenses in response to reduced oxygen transmission to the cornea resulting in encroachment of blood vessels into the cornea.
Neurons
Cells which transmit information by electrical or chemical stimulation. They form the core components of the peripheral and central nervous systems and are responsible for stimulus of the sensory organs.
Nickel
A metal commonly used as an alloy in metal spectacle frames.
Nose pad
Small supports attached to a spectacle frame to rest frame comfortably on the nose.
Nystagmus
Uncontrolled movement of the eye that is rapid and repetitive. The eyes may swing side to side, up and down or in a circular motion. It is often associated with poor visual acuity.
Laser Eye Surgery Terms Beginning with 'O'
Ocular herpes
Herpes of the eye occurs when herpes simplex virus infects the eye. It usually affects the cornea causing inflammation of the tissue. If it occurs in the superficial layers of the cornea it may heal without scarring but if it affects the deeper layers it may scar and lead to loss of vision. Less commonly ocular herpes can affect the structures inside the eye.
Ocular hypertension
Abnormally raised Intraocular pressure in absence of damage to the optic nerve or reduction in the field. Patients with ocular hypertension have a greater tendency to develop glaucoma.
Ocular migraine
Visual disturbances characteristic of migraine without developing the actual headache.
OD
Abbreviation for Oculus Dexter which means Right Eye in Latin.
Ophthalmologist
Specialist in medical eye conditions and eye surgery.
Ophthalmoplegia
Paralysis or weakness of the eye muscles. It is often caued by neurological disorders. It causes limitation of muscle function which can in turn result in diplopia, ptosis and nystagmus.
Optic nerve
Transmits information from the retina to the brain. Photoreceptor cells in the retina respond to light stimulation sending electrical impulses along the optic nerve to the visual cortex where they are  interpreted as vision.
Optic nerve head
Pale disc shaped area on the retina where the ganglion cells exit the eye to form the optic nerve. It is also referred to as the optic disc. As it does not contain any photoreceptors it is the source of the blind spot which naturally occurs in our field of vision.
Optical coherence tomography
3D imaging of biological tissue using near infra-red light. It is used in ophthalmology to obtain detailed images within the retina.
Optician
Generally refers to somone who dispenses spectacles and contact lenses.
Optics
Study of maths and physics of properties of light.
Optometrist
Health care professional concerned with vision, the eye and related structures.
Orbit
The cavity or socket in the skull in which the eyeball is located.
Orthokeratology (ortho-k)
Correction of myopia using rigid contact lens worn overnight to reshape the cornea.
OS
Abbreviation of Oculus Sinister, which means Left Eye in Latin.
OU
Abbreviation of Oculus Uterque, which means Each Eye and Oculi Unitas which means Both Eyes in Latin.
Overconvergence
Eye muscle imbalance where there is excessive convergence of one or both eyes which can result in diplopia and suppression of image from one eye.
Overflow tearing
Occurs due to impaired drainage of tears away from the eye through the lacrimal duct as new tears are produced by glands in the eyelids. This overflow can be due to a blocked duct, loss of tension in the eyelids, or poor tear quality.
Laser Eye Surgery Terms Beginning with 'P'
Papilla
Small elevation at the optic disc.
Papilloedema
Swelling of the optic disc usually occurs bilaterally and is due to raised intracranial pressure. It does not normally affect visual acuity in acute phase but can damage peripheral field of vision.
Papilloma
Benign epithelial growth on the skin which projects outwards in frond-like appearance.
Pars plana
It is part of the ciliary body forming the area where sclera and the iris meet on the inside of the eye.
Penetrating keratoplasty
This is a surgical procedure whereby damaged or diseased corneal tissue is replaced by donated tissue as a graft.
Peripheral vision
Part of the visual field that results from light stimulating the retina outside the fovea.
Phacoemulsification
The lens in the eye is broken down within the capsule in which resides an ultra-sonic device. The lens pieces are then removed by an aspirator which suctions them out. The lens can then be replaced by injecting a new synthetic lens in its place.
Phakic
An eye which retains a natural crystalline lens.
Phoropter
An instrument containing different lenses in graduated powers which can be turned in place in mixture of spherical and cylindrical powers to refract the eye and determine correction needed.
Photoablation
The vaporization of tissue by a laser using ultra-violet light.
Photochromic
Lenses that darken in the presence of UV light.
Photocoagulation
The clotting of tissue using a laser which emits light in a specific wavelength. Haemoglobin, a pigment in blood, selectively absorbs light from the visible green wavelength. Lasers which emit light of this wavelength are used to seal off blood vessels in this way. This technique is used to treat abnormal proliferation of blood vessels in the retina, detached retina and shrink tumours by cutting off their blood supply.
Photokeratitis
A painful condition caused by over exposure of the eyes to UV radiation. Symptoms include photophobia and pain and temporary loss of vision due to damage to the corneal surface.
Photophobia
Excessive sensitivity to light causing tearing, pain or discomfort in presence of natural or artificial light.
Photopsia
Sparks or flashes of light which are not visual in origin but in fact are due to mechanical stimulation of the light receptors in the retina. It is often associated with post vitreous detachment or retinal detachment. It is also a feature of visual disturbance associated with migraine.
Photoreceptor
Specialized nerve cell found in the retina able to convert light into an electrical impulse. The two principal photoreceptors are the rods and cones.
Phytochemicals
Chemical compounds that naturally occur in plants that appear to help protect humans against disease and cancer.
Pinguecula
A common benign growth on the conjunctiva. It often appears as a yellowish, nodular, thickened lesion on the sclera near the cornea.
Placebo
A treatment that has no intrinsic value in itself but is used in trials to compare effectiveness of actual treatment to the "pretend treatment".
Plano
Literally meaning "flat" this term is used to describe an optical lens that has no focussing power.
PMMA (polymethyl methacrylate)
A transparent thermoplastic which was the original material used to produce rigid contact lenses referred to as hard contact lenses.
Polarized lenses
Lenses which filter light which is oscilliating in a given direction. This principle is used to filter light from sources such as bodies of water to reduce reflections which would cause glare.
Polycarbonate
A thermo-plastic polymer used in the manufacture of optical lenses and spectacle frames.
Porphyria
A relatively uncommon condition whereby an over production of chemicals called porphyrin accumulate in the body. Symptoms include urine appearing red in colour, abdominal pain, and damage to the skin as it comes to sunlight and more prone to injury.
Posterior chamber
The space in the eye between the posterior surface of the iris and ciliary body and anterior to the lens.
Presbyope
Patient who has reduced ability to read due to loss of accommodation.
Presbyopia
Diminished ability to focus at near which is age related. It occurs due to loss of power in the ciliary body and reduced elasticity of the crystalline lens.
Prescription lenses
Optical lenses that have been designed to correct vision with the appropriate power as indicated by prescription from Optometrist or Ophthalmologist.
Prism
Prisms are incorporated in to spectacle lenses to correct muscle imbalances between the eyes. The prism is used to deflect light to alter the position of the image source with respect to the visual axis. They are often used to correct diplopia.
PRK (Photorefractive Keratectomy)
A form of refractive surgery in which the epithelial cells are abraded from the corneal surface and then an excimer laser is used to reshape the underlying corneal tissue. Recovery is slow and painful. There is a significant risk of haze developing in the treated area.
Progressive lenses
Also referred to as varifocal or multifocal lenses. They are characterized by a gradient of increasing power with correction for distance vision at the top of the lens gradually changing in power to correction for near at the bottom part of the lens. They are used to correct vision when patient develops presbyopia.
Proliferative vitreoretinopathy (PVR)
A complication that commonly develops secondary to retinal detachment. It causes scar tissue to form in sheets which contracts and distorts the retina.
Prosthetic
Refers to an artificial device which replaces a body part e.g. "a glass eye".
Protective eyewear
Spectacles or goggles designed to from special materials to protect the eyes from injury.
Protein
Biochemical compounds found in the body necessary for cell growth and repair. Protein can be deposited by the tears onto contact lenses causing discomfort in lens wear.
Pseudoexfoliation syndrome
Characterized by deposits of white fibrillogranular material on the anterior lens capsule at the pupil margin. It is considered to be one of the most common causes of glaucoma due to accumulation of pseudoexfoliate material in the trabecular meshwork.
Pseudotumor cerebri
A neurological condition characterized by raised intra-cranial pressure in the absence of a tumour. Common symptoms include nausea, headaches, vomiting and tinnitus. Untreated it can cause vision loss due to swelling of the optic disc. It most commonly occurs in young obese women.
Pterygium
A benign wedge-shaped growth of the conjunctiva on the sclera. It may cause no symptoms or become inflamed causing itchiness and burning sensation. It is most commonly found in people who are more exposed to sunlight and wind. If it grows into the cornea it may be removed surgically.
Ptosis
Condition in which one or both eyelids droop. It may be due to weakness of the muscle in the upper eyelid, damage to the nerves controlling this muscle or loosening of the tissue in the lid. It can be caused by the aging process, a congenital abnormality or the result of injury or disease.
Puncta
Minute openings located nasally on the lid margins. Tears are drained through these openings into the lacrimal duct.
Punctal plugs
Small collagen or silicone plugs designed to be inserted in the puncta to block the tear duct. They are used to treat moderate to severe dry eye problems on the basis that they keep tears in the eye for longer periods of time.
Pupil
Aperture at the centre of the iris which controls light entering the eye.
Pupillary distance
Distance between the centres of the pupils in each eye. It is used to position the focal centre of spectacle lenses appropriately for comfortable vision.
Laser Eye Surgery Terms Beginning with 'Q'
We're sorry, but we haven't added any laser eye surgery terms beginning with the letter 'Q' to the glossary.
Laser Eye Surgery Terms Beginning with 'R'
Re-treatment
See enhancement.
Reading glasses
Glasses that magnify for close work or reading. Reading glasses are prescribed for people who are presbyopic.
Refraction
The change in direction of light rays as they strike the interface between two materials of different refractive index. A measurement of the focusing power of the eye; to determine what power of optical aids are necessary to fully correct an ametrope.
Refractive Error
An assessment of the degree of ametropia that results in light being focused away from the retina, by the refractive elements of the eye. Measured in dioptres, it is an indication of the severity of myopia, hypermetropia or astigmatism in an eye.
Refractive Lens Exchange
Or Clear Lens Extraction, is a procedure in which the natural crystalline lens in the eye is removed and replaced with an artificial, silicon, intraocular lens of specific power, to correct the refractive error of the eye. The procedure is similar to cataract surgery.
Refractive surgery
Any type of surgical treatment that changes the ability of the eye to focus light, with the intention of reducing any ametropia present. There are various corneal and intraocular treatments available, including LASIK, LASEK, PRK, Intacs, ICL, ICRS, CLE or RLE.
Regression
Post refractive surgery, natural changes in the eye can induce a refractive error. In most cases an enhancement procedure can be performed to return the eye to an emmetropic state.
Retina
A complex structure of multiple layers of various types of cells, found on the inner, back surface of the eye. Photoreceptors are responsible for detecting light incident on the retina. Various other cells and processes are involved in converting light energy into electrical impulses that are transmitted to the occipital lobe of the brain, via the optic nerve, to be processed for visual perception.
Retinal detachment
A condition in which the neurosensory layers of the retina separate from the retinal pigment epithelium (RPE), allowing vitreous fluid to enter the sub-retinal space. The cells in the detached part of the retina are no longer able to derive nutrients from the choroid and this can result in permanent blindness if the retina is not re-attached early enough. The older population and highly myopic eyes are more susceptible to detachments. They are often caused by head trauma and sudden harsh movements such as in bungee jumping. Diseases such as diabetic retinopathy and scleritis can also increase the risk of retinal detachments.
Retinal Pigment Epithelium (RPE)
A single layer of hexagonally shaped, pigmented, epithelium cells, forming a boundary between the sensory retina and the choroid. The pigmented cells absorb stray light, preventing any further scattering in the eye. They phagocytose dead and damaged photoreceptor cells from the retina and also store Vitamin A for the photoreceptors. The RPE acts as a limiting membrane, controlling the movement of substances between the retina and choroid.
Retinitis Pigmentosa
The term given to a large group of hereditary conditions that are characterized by progressive retinal degeneration, also known as rod-cone dystrophies. It is believed that abnormal production of photoreceptor proteins are the root cause. Most common symptoms include nyctalopia (dark adaptation problems), photophobia, 'tunnel vision' and decreased central vision.
Retinopathy of Prematurity
A disease affecting prematurely born infants, characterized by abnormal, disorganized growth of retinal vasculature. It is most commonly asymptomatic but can result in permanent loss of vision.
Retinoschisis
Abnormal splitting of the retinal layers. Classified as either acquired or juvenile Retinoschisis. The former being a degenerative process characterized by separation of the inner nuclear and outer plexiform layers. The latter, a congenital process characterized by splitting within the nerve fibre layer.
RGP
Or Rigid Gas Permeable lenses, are a type of contact lens manufactured from oxygen permeable polymers. They are made to custom specifications for each individual eye and when correctly fitted, they encourage the cornea to take up a more regular shape, resulting in a good level of visual acuity for individuals with high degrees of astigmatism or with irregularly shaped corneas induced by conditions such as keratoconus.
Rhegmatogenous Retinal Detachment
A type of retinal detachment as a result of a break in the retina, allowing vitreous fluid to enter the space between the neurosensory retina and the retinal pigment epithelium (RPE).
Rheopheresis
An experimental treatment for Age Related Macular Degeneration (ARMD) based on apheresis, in which the blood of the subject is filtered to remove large proteins and cholesterol to improve the blood circulation to cells in the macula of the eye.
Rheumatoid Arthritis
An inflammatory disorder of the joints. Symptoms vary but include pain and swelling in joints and stiffness. It is an autoimmune disease which can have complications requiring treatment with an Ophthalmologist and is associated with Sjogren syndrome. There is no cure but early, aggressive treatment to manage future symptoms is important.
River Blindness
Also known as Onchocerciasis or Robles' Disease, is a parasitic disease where the Onchocerca volvulus infects the patient through the bites of the blackflies of Simulium species which are carriers of its larvae. According to the WHO, it is prevalent in many African countries as well as in Latin America. The eye lesions manifest in inner tissues of the eye and cause inflammation, bleeding and blindness if untreated. Mectizan® is currently used as a treatment over prolonged periods to avoid complications and prevent blindness.
RK
RK (Radial Keratotomy) is a surgical procedure used to treat patients with moderate myopia. Deep corneal incisions are made with a diamond knife with an aim to flatten the central cornea. It is rarely ever used anymore owing to far more sophisticated techniques and with fewer complications being developed to correct myopia.
Rod
A type of photoreceptor cell found in the retina, that facilitates the detection of light in scotopic (low light) conditions.
Laser Eye Surgery Terms Beginning with 'S'
Sarcoidosis
Idiopathic multisystem disease which forms in the lymph nodes, lungs, skin and other areas including eyelid skin, lacrimal gland and sac and nasolacrimal duct. Symptoms include fatigue, weight loss, fever, coughing, uveitis, cranial nerve palsies and skin lesions. Some patients also develop dry eyes. May cause redness, pain, swelling of involved lids or lacrimal glands, painless subcutaneous nodular masses in eyelids, ptosis, diplopia, sever cicatrizing conjunctival inflammation, conjunctival nodules, keratoconjunctivitis sicca, band keratopathy, cataract, chorioretinitis, retinal periphlebitis or neovascularisation, optic nerve disease, glaucoma or orbital involvement. Prognosis varies depending on the tissues involved.
Schlemm's Canal
A porous channel at the iridocorneal angle into which the aqueous humour flows via a network of trabeculae. The canal empties into exrtaocular veins. It is itself a vein with thin walls and a very porous endothelial membrane and extends all around the circumference of the eye. When drainage is blocked, there is increased resistance to the flow of fluid through the trabeculae into the canal of Schlemm and abnormally high pressure manifests, being the underlying pathology for most presentations of glaucoma.
Sclera
The fibrous layer forming the outermost covering of the eye is composed of connective tissue and has two regions - the cornea and the sclera. The sclera forms the posterior region of this dense avascular tissue and is seen as the opaque white of the eye.
Scleritis
Inflammation of the sclera which can occur both in anterior or posterior regions. It is known to be associated with systemic disease in about half of patients. Symptoms include pain, swelling, red eyes, photophobia and decreased vision and it is found to be bilateral in over 50% of presentations. Treatment varies with severity and referral to a uveitis specialist may be required. It can be a recurrent condition.
Scotoma
A region of visual field loss (blind spot) within outer relatively normal vision. It is commonly seen after a stroke or brain injury and can be indicative of optic nerve damage. There are different types of pathological scotomas such as central, hemianopic, peripheral and pareacentral which vary in the location and effect on daily life of the blind spot.
Seborrheic Dermatitis
A common skin condition which is inflammatory and results in the formation of 'scales' on oily areas of the scalp and inner ear. It is present with redness and itching. It is linked to blepharitis where there can be bacterial growth around the eyelids and the dermatitis exacerbates the colonisation of the lid margin.
Segment
A 'part' such as the near-vision hemispheric portion of a pair of bifocal lenses in frames.
Silicone
A synthetic polymer which is frequently used to manufacture the nose pads of spectacle frames. Some people may have allergies to it and should notify their practitioners so that an alternative can be provided.
Single Vision
A type of optical lens which has the same 'power' throughout the lens in contrast to bifocal or multifocal spectacle lenses.
Sinusitis
An inflammation of the mucosal lining of the sinuses of which humans have four pairs - the frontal, maxillary, ethmoid and sphenoid. It is often a result of an infection and can be termed acute or chronic. Symptoms include pressure and pain around the nasal area, blocked nose with discharge (can lead to sore throats and spread of the infection) and headaches. Sinus infections can cause complications if they spread and can underlie symptoms such as exophthalmos (protruding eyes) owing to orbital cellulitis as a result of infection in the ethmoid sinuses.
Sjorgen Syndrome
An autoimmune disorder involved with a type of dry eye disease termed 'aqueous deficient dry eye'. It leads to lacrimal gland dysfunction and a reduced tear production. Symptoms are dry eyes, dry mouth and usually includes an inflammatory component. Corneal ulcers can be one of the complications of the condition and although there is no cure, symptoms can be managed with eye drops and medicines.
Skin Cancer
A broad title to indicate the uncontrolled growth of abnormal skin cells. If untreated, the cancer cells then spread to other tissues of the body. Different types of skin cancer include basal cell carcinoma, squamous cell carcinoma and melanoma (which although less common is more dangerous and the leading cause of mortality for skin cancer patients). Various factors are involved in the incidence of skin cancer such as genetic predisposition, age, lighter complexion and the widely publicized damage by UV sun exposure. Symptoms vary greatly but features to look out for include the asymmetry, borders, colour and diameter of the abnormal area or mole. Surgical intervention is common if caught early but prognosis varies across different cases.
Snellen Visual Acuity Test
A very common method of measuring a subject's vision or visual acuity. The test chart consists of lines of letters of varying size and spacing, with the largest letter at the top and a gradual progression down to the smallest letters at the bottom. The test is carried out at a distance of 6 metres and the result is recorded as a Snellen fraction. E.g. 6/9, which suggests that at a distance of 6 metres, the subject is able to see an object with the same clarity as the 'standard observer' viewing the same object at a distance of 9 metres.
Soft contact lenses
The most common type of contact lens manufactured using various similar materials of varying water content and permeability.
Solution
Broad term referring to various products that are used to clean, disinfect and store contact lenses.
Spatial Frequency
A measure of how often sinusoidal components of a structure repeat per unit of distance.
SPF
The Sun Protection Factor is a measurement used to represent how much protection a product such as sun-screen provides when applied to skin.
Spherical
Refers to the lens form of a spectacle lens or contact lens. As the name suggests, this type of lens only incorporates a spherical power and does not have a cylindrical component.
Spherical Aberration
The first of the Seidal Aberrations, is a result of paraxial rays of light coming to a focus at a different position to the central rays of light when refracted or reflected by an optical medium. This is commonly seen by spectacle wearers as halos or glare around bright lights. This type of aberration can be minimized by the use of aspheric lenses.
Spots
With respect to the eyes, spots refers to small particulate specks which are noticeable to the patient when they appear within the line of sight and seem to be drifting across their vision. The underlying cause is thought to be the visible collagen of the vitreous as it ages, moving as the eye moves. It is medically feasible to eliminate these via a vitrectomy (surgical operation to remove the vitreous humour of the eye) but this carries significant risks and possible complications and is generally ill-advised. See 'floaters'.
Spring Hinge
This is a kind of manufactured hinge for spectacle frames which tends to be more flexible than standard hinges so as to offer better durability for the spectacles.
Starbursts
A complication caused by older, less advanced Lasers and techniques. Subjects complain of halos or streaks of light emerging from bright light sources. These are most common in subjects with large pupils and is compounded in low light conditions. It is widely recognized as a result of inadequate, small treatment zones.
Stereopsis
Essentially refers to 3D vision. It is the term used to describe the visual process whereby the brain 'fuses' the two images received from each eye which are technically perceived from slightly different vantage points, allowing us to have perception of depth. Stereoacuity is generally tested with Titmus or Randot tests.
Strabismus
Broadly defined as a misalignment of the eyes (they can't point at a single object or focus together). It may be horizontal, vertical or comitant or incomitant, latent, manifest or intermittent. Phoria describes a latent deviation and Tropia the manifest deviations. Esotropia is inward deviation (crossed-eyes), exotropia is outward deviation. Hypertropia is upward deviation and hypotropia downward. Esotropia is a type of horizontal strabismus which is considered most common and can be infantile. Occlusive therapy is generally used to treat the amblyopia before considering surgery. Muscle surgery is recommended to be performed within 6 months to 2 years of age. There are other forms of esotropia such as accommodative, acquired nonaccommodative and cyclical esotropia. Exotropia can be intermittent or constant and treatment involves corrective prisms and monocular occlusion. Muscle surgery may be considered. Vertical strabismus include Brown's Syndrome and Double Elevator Palsy of which there are three types; Duane's Retraction Syndrome and Mobius' Syndrome are also forms of strabismus.
Stroke
As a result of hypertension (high blood pressure) the mean arterial pressure of the patient is greater than the upper range of the accepted normal ranges. This high pressure can rupture major blood vessels in the brain and cause tissue death termed a 'cerebral infarct' or a stroke. The prognosis varies depending on which part of the brain tissue is involved, but can include dementia, blindness, paralysis and other complications.
Stromal Tissue (Corneal)
A layer of tissue found between Bowman's Membrane and Decemet's Membrane, making up approximately 90% of the corneal thickness. It is composed mainly of collagen fibrils that have a specific, uniform arrangement that make the cornea transparent. Excimer lasers target the removal of this tissue to create changes in the shape of the cornea.
Sty
A bacterial infection of a sebaceous gland in the eyelid or gland of Zeis or Moll. It usually manifests as a subcutaneous nodule (red lump in the eyelid) and can leak fluid. It can be painful and swollen and occasionally can be associated with meibomitis or rosacea.
Subconjunctival Hemorrhage
A term describing bleeding from blood vessels just below the surface of the sclera. It can usually be seen as a red patch, and can take up to a few weeks to subside depending on the extent of damage to the blood vessels. It can be caused by sudden trauma to the head, sneezing, coughing or high blood pressure.
Superior Limbic Keratoconjunctivitis
A type of chronic conjunctivitis which is seen to be prevalent in middle aged females, particularly with underlying thyroid dysfunction pathology. The superior limbus (at junction of the cornea and sclera), the conjunctiva lining it and the eyelid are inflamed. Often no discharge is observed. It may be brought on by sensitivity to contact lens use in which case this should be stopped or contact lens solutions containing no preservatives be used. In chronic persistent cases, topical steroids may be considered or silver nitrate/cromolyn sodium solution prescribed.
Surgery Complication
All forms of surgery carry risk factors and it is important to consider these in every individual case, particularly elective procedures. Complications may arise during the procedure itself or post-operatively. In ophthalmic surgeries such as for cataracts or LASIK, the most common complications include post-op infections and related poor healing issues, which are generally temporary if managed properly alongside good patient compliance. All surgical procedures would require the patient to sign consent forms and during the process of consent, all risks and contraindications should be explained and addressed. Any further advice should be sought from the practitioner and surgeon in an in-depth consultation.
Suspensory Ligament
The Zonules of Zinn are fibres that connect the ciliary body to the crystalline lens of the eye.
Laser Eye Surgery Terms Beginning with 'T'
Tay-Sachs disease
Also known as Gangliosidosis Type II, is a hereditary (autosomal recessive) disorder owing to a genetic defect on chromosome 15, characterized by a lack of hexosaminidase A which is an enzyme involved in nerve tissue metabolism. The disease is found to be common amongst the Jewish Ashkenazi population. Symptoms vary between its infantile and adult forms however it does have retinal and optic nerve involvement. A prominent 'cherry-red spot' is generally found on the retinal scan as a result of lipid storage dysfunction in the retinal ganglion cells and the disorder can cause blindness, deafness, seizures and loss of muscle function.
Thrombosis
The formation of a blood clot inside any vasculature in the body, restricting the flow of blood through the affected area.
Titanium
A very popular metal used in the manufacture of spectacle frames due to its lightweight, strong and hypoallergenic properties.
Tonic Pupil
A condition in which parasympathetic denervation to the pupil causes it to be less responsive to light and thus is not able to constrict appropriately.
Topography (Corneal)
A non evasive, diagnostic tool that creates a digital map of the curvature of the corneal surface. The data is vital in diagnosing and monitoring various corneal abnormalities, such as Keratoconus. Since the cornea is responsible for approximately 70% of the eye's refractive power, it is essential to capture corneal data of this nature before any course of refractive treatment can be decided on. The corneal topography is used by excimer lasers during LASIK treatments.
Toric
A type of lens used to correct astigmatism, that incorporates two different powers perpendicular to each other, giving the lens a spherical and cylindrical component. There are different toroidal designs such as tyre, barrel and capstan formations.
Toxocariasis
An infection caused by the larvae of the roundworm Toxocara canis. Yellowish white granulomas form, often unilaterally. It is associated with papillitis and retinal detachments amongst other scars can remain even after the infection.
Toxoplasmosis
A form of retinitis with parasitic innervation - Taxoplasma gondii. It may be congenital or acquired (usually from poorly cooked meat). Symptoms and lesions formed vary between the two forms but retinal necrosis occurs in both. There is a poorer prognosis with larger lesions if located closer to the fovea and optic nerve.
Trabecular Meshwork
Spongy tissue lined with trabeculocytes, that facilitates drainage of aqueous fluid between the anterior chamber and Canal of Schlemm. There are three layers of meshwork, the inner uveal meshwork, the corneoscleral meshwork and the juxtacanalicular tissue.
Trachoma
A type of chronic infectious conjunctivitis that can be chlamydial. Upper tarsal scarring may be observed with concretions as well as Herbert's pits. Good hygiene and clean water should be prescribed as preventative measures and antibiotics may be used to treat in early stages. Eventually the scarred eyelid may turn inwards causing further trauma to the cornea and can have greater visual loss implications. This can be surgically rectified.
Transient Ischemic Attack (TIA)
Sometimes called a 'ministroke', this refers to a change in the blood supply to a particular area of the brain. A TIA can cause fluctuation in vision as well as other symptoms associated with strokes such as paralysis of one side of the body, slurring of speech or dizziness.
Trauma
A very broad term referring to any injury as a result of a sudden violence. Trauma to the head can often cause problems with the eyes resulting in loss of vision, blurry vision, double vision, swelling, iris defects and 'black eyes'.
Trichiasis
The eyelashes grow towards the eye and can cause irritation and scarring in very serious cases.
Trichotillomania
A condition characterized by compulsive pulling of hair or eyelashes by the subject.
Trifocal
A type of lens that has three areas, each of a different power, to give the patient optimal vision for distance, intermediate and reading. The power for each part of the lens is prescribed by an optometrist.
Laser Eye Surgery Terms Beginning with 'U'
Ultraviolet Light
UV light refers the a part of the electromagnetic spectrum just outside of the visible spectrum. UV light has shorter wavelength than visible light, but longer wavelength than X-Rays. UV light is known to be harmful to the skin and eyes.
Uvea
The uveal tract consists of the iris, ciliary body and choroid.
Uveitis
A broad term characterized by inflammation of the uvea. Symptoms include asthenopia, tearing, redness, increased photosensitivity, poor vision and floaters. Some common types of Uveitis are iritis, iridocyclitis, cyclitis, pars planitis and choroiditis.
Laser Eye Surgery Terms Beginning with 'V'
Vascular Problem
A broad term collectively representing any problem or condition affecting the body's vascular system. This can include high blood pressure, a clot, an aneurysm, an embolus. Vascular problems can often have an effect on the eyes, and can cause asthenopia and loss of vision.
Vergence Disorder
A range of conditions referring to the inability of the eye to either turn inwards or outwards. Common symptoms of vergence disorders include asthenopia and double vision.
Vision
This refers to Uncorrected Visual Acuity (UCVA). It is determined by the smallest line of letters or symbols that an uncorrected ametrope can correctly identify on a test chart.
Visual Acuity
This refers to Best Corrected Visual Acuity (BCVA). It is determined by the smallest line of letters or symbols that a fully corrected ametrope or emmetrope can correctly identify on a test chart.
Visual Field
This is the total area a person is able to see when their eyes are fixating on an object. The 'standard observer' has a visual field stretching approximately 60° nasally, 100° temporally, 60° superiorly and 75° inferiorly in each eye.
Vitrector
A very small motorized instrument that is used in surgical procedures to extract the vitreous fluid during a vitrectomy.
Vitreous Body
The posterior chamber of the eye, between the lens and the retina, is filled with a clear jelly like fluid known as the vitreous humor.
Vitreous Detachment (posterior vitreous detachment)
Condition in which the vitreous collapses and separates from the macula and optic disc. It may be localized or total. It is usually caused by aging where the vitreous is liquefied and can also occur more prematurely after cases of trauma, cataract surgery or in patients presenting diabetes mellitus and retinitis pigmentosa.
Vitreous Hemorrhage
Broadly encompasses the presence of blood in the vitreous space. Its symptoms include sudden appearance of floaters or spots and drop in visual acuity. Upon examination there may be a diminished or no view of the fundus in which case ultrasonography may be required to eliminate retinal detachment. It may be caused by a range of underlying issues such as ruptured retinal vessels, diabetic retinopathy, sickle cell retinopathy, Terson's syndrome, Eales' disease, hypertensive retinopathy and others.
Laser Eye Surgery Terms Beginning with 'W'
We're sorry, but we haven't added any laser eye surgery terms beginning with the letter 'W' to the glossary.
Laser Eye Surgery Terms Beginning with 'X'
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Laser Eye Surgery Terms Beginning with 'Y'
We're sorry, but we haven't added any laser eye surgery terms beginning with the letter 'Y' to the glossary.
Laser Eye Surgery Terms Beginning with 'Z'
We're sorry, but we haven't added any laser eye surgery terms beginning with the letter 'Z' to the glossary.