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Glossary of Terms



A cell designed for the storage of fat, found in connective tissue.

Age-Related Macular Degeneration (AMD, ARMD)
A group of conditions that include deterioration of the macula, resulting in loss of sharp central
vision. There are two general types: “dry,” which is more common, and “wet,” in which abnormal
new blood vessels grow under the retina and leak fluid and blood (neovascularization), further
disturbing macular function. AMD is the most common cause of decreased vision after age 60.

Amblyopia (Lazy Eye)
Decreased vision in one or both eyes without detectable anatomic damage in the eye or visual
pathways. Amblyopia is usually uncorrectable with corrective lenses.

Amsler Grid
A test card or grid (black lines on white background or white lines on black background) used for
detecting central visual field distortions or defects, such as in macular degeneration.

The formation of new blood vessels, especially blood vessels that supply oxygen and nutrients to
cancerous tissues.

The administration of gases or the injection of drugs before surgical operations to create
insensitivity to pain.

Anterior Chamber
The fluid-filled space inside the eye between the iris and the innermost corneal surface

The absence of the lens of the eye, due to surgical removal, a perforating wound or ulcer, or
congenital anomaly. It causes a loss of accommodation, far sightedness (hyperopia), and a deep
anterior chamber.

A type of ultrasound, radar-like device that emits very high frequency waves that are reflected by
the various parts of the eye and converted into electrical impulses. A-scans are used for
differentiating between normal and abnormal eye tissue, or for measuring the length of the

A collection of symptoms producing eye fatigue or tiredness. Pain or headaches may also occur.
Asthenopia is sometimes caused by uncorrected refractive errors.

An optical defect in which refractive power is not uniform in all directions (meridians). Light rays
entering the eye are bent unequally by different meridians, which prevents formation of a sharp
image focus on the retina. Slight uncorrected astigmatism may not cause symptoms, but a large
amount may result in significant blurring and headache.

Autosomal Dominant
One of several ways that a trait or disorder can be passed down through families. If a disease is
autosomal dominant, it means you only need to get the abnormal gene from one parent in order
for you to inherit the disease. One of the parents may often have the disease.

A drug that slows the growth of new blood vessels. It is licensed to treat various cancers,
including colorectal, lung, breast (outside the USA), glioblastoma (USA only), kidney and ovarian.


Corrective lenses with two parts of different focal lengths, one for distant vision and one for near
vision. (Usually of a pair of eyeglasses)

Binocular Vision
The blending of the separate images seen by each eye into one composite image.

Black Eye
A bruised discoloration of the flesh surrounding the eye, often resulting from a blow.

Inflammation of the eyelids, usually with redness, swelling, and itching.

Blind Spot
Sightless area within the visual field of a normal eye caused by absence of light sensitive
photoreceptors where the optic nerve enters the eye.

A type of ultrasound which provides a cross-section view of tissues that cannot be seen directly.
High frequency waves are reflected by eye tissues and orbital structures and converted into
electrical pulses, which are displayed on a printout.

Latin term for “bubble.”

Bullous Keratopathy
Corneal edema characterized by the formation of large subepithelial bullae that cause intense
pain when they rupture and expose corneal nerves.


Opacity or cloudiness of the crystalline lens, which may prevent a clear image from forming on
the retina. Surgical removal of the lens may be necessary if visual loss becomes significant, with
lost optical power replaced with an intraocular lens, contact lens, or aphakic spectacles.
Cataracts may be congenital or caused by trauma, disease, or age.

Cataract Extraction
The removal of a cloudy lens from the eye. An extracapsular cataract extraction leaves the rear
lens capsule intact; with an intracapsular extraction there is complete removal of a lens with its
capsule, usually by cryoextraction.

Chalazion (Internal Hordeolum)
An inflamed lump in a meibomian gland (in the eyelid). Inflammation usually subsides, but the
lump may need surgical removal.

The vascular (major blood vessel) layer of the eye lying between the retina and the sclera. The
choroid provides nourishment to outer layers of the retina.

Color Blindness
A reduced ability to discriminate between colors, especially shades of red and green. It is usually

A light-sensitive retinal receptor cell that provides sharp visual acuity and color discrimination.

The transparent mucous membrane covering the outer surface of the eyeball except the cornea,
and lining the inner surfaces of the eyelids.

Conjunctivitis (Pink Eye)
Inflammation of the conjunctiva characterized by discharge, grittiness, redness and swelling.
Usually viral in origin, it may be bacterial or allergic, and may be contagious.

The inward movement of both eyes toward each other, usually in an effort to maintain single
binocular vision as an object approaches.

A condition that is present from birth (especially of a disease or physical abnormality).

The transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides
most of an eye’s optical power.

Corneal Abrasion
A corneal abrasion is a worn or scraped-off area of the outer, clear layer of the eye (cornea).

Corneal Edema
A swelling of the eye’s cornea; causes include intraocular surgery, corneal dystrophies, high
intraocular pressure and contact lens complications. Symptoms include vision loss, halos around
lights, a white or cloudy spot on the eye, photophobia, eye pain and foreign body sensation.

See esotropia.

Crystalline Lens
The transparent elastic structure behind the iris by which light is focused onto the retina of the eye.


Dyslipidemia is an abnormal amount of lipids (e.g. cholesterol and/or fat) in the blood. In
developed countries, most dyslipidemias are hyperlipidemias; that is, an elevation of lipids in the
blood. This is often due to diet and lifestyle.

A metabolic disease in which the bodyʼs inability to produce any or enough insulin causes
elevated levels of glucose in the blood. This can contribute to vision problems such as diabetic

Diabetic Retinopathy
The spectrum of retinal changes accompanying long-standing diabetes mellitus. The early stage
is background retinopathy , which may advance to proliferative retinopathy , including the growth of
abnormal new blood vessels (neovascularization) and fibrous tissue.

Dilated Pupil
An enlarged pupil, resulting from contraction of the dilator muscle or relaxation of the iris sphincter.
It occurs normally in dim illumination, or it may be produced by certain drugs (mydriatics,
cycloplegics) for the purpose of an eye exam, or result from blunt trauma.

The unit to designate the refractive power of a lens.

Diplopia (Double Vision)
The perception of two images from one object; images may be horizontal, vertical or diagonal.

Tiny, white hyaline deposits on Bruchʼ s membrane (of the retinal pigment epithelium). Becomes
common after age 60; can sometimes be an early sign of macular degeneration.

Dry Eye Syndrome
Corneal and conjunctival dryness due to deficient tear production, predominantly in menopausal
and post-menopausal women. It can cause foreign body sensation, burning eyes, filamentary
keratitis, and erosion of conjunctival and corneal epithelium.


The thin layer of cells that lines the interior surface of blood vessels and lymphatic vessels,
forming an interface between circulating blood or lymph in the lumen and the rest of the vessel

The inward turning of an upper or lower eyelid so that the lid margin rests against and rubs the

Esotropia (Cross-eyes)
Eye misalignment in which one eye deviates inward (toward nose) while the other fixates

Excimer Laser
A class of ultraviolet lasers that removes tissue accurately without heating it. Used in refractive
corneal surgery, the laser is controlled by computer to make precise pre-programmed shavings of
eye tissue to produce a given optical correction. It is used for photorefractive keratectomy (PRK),
and combined with automated lamellar keratoplasty (ALK) to produce LASIK (laser in situ

Exotropia (Wall-eyes)
Eye misalignment in which one eye deviates outward (away from nose) while the other fixates

Extraocular Muscles
The six muscles that move the eyeball (lateral rectus, medial rectus, superior oblique, inferior
oblique, superior rectus, inferior rectus).

Structures covering the front of the eye which protect it, limit the amount of light entering the pupil,
and distribute tear film over the exposed corneal surface.


The central pit in the macula that produces the sharpest vision. It contains a high concentration of
cones and no retinal blood vessels.

Fuchs Endothelial Dystrophy (Fuchs’ Corneal Endothelial Dystrophy or FCED)
A condition that causes vision problems. The first symptom of this condition is typically blurred
vision in the morning that usually clears during the day. Over time, affected individuals lose the
ability to see details (visual acuity). People with Fuchs endothelial dystrophy also become
sensitive to bright lights.

The interior posterior surface of the eyeball; includes the retina, optic disk, macula, and posterior
pole. The fundus can be seen with an ophthalmoscope.

Fusional Amplitude
The maximum amount of eye movement produced by fusional vergence, the movement of both
eyes that enables the fusion of monocular images providing binocular vision.

Fusional Vergence
The movement of both eyes that enables the fusion of monocular images providing binocular


A group of diseases characterized by increased intraocular pressure resulting in damage to the
optic nerve and retinal nerve fibers. Glaucoma is a common cause of preventable vision loss, and
may be treated by prescription drugs or surgery.

Examination of the anterior chamber angle through a goniolens (special type of contact lens).


Hyperopia (Farsightedness)
A focusing defect in which an eye is underpowered. Light rays coming from a distant object strike
the retina before coming to sharp focus, blurring vision. Hyperopia can be corrected with
additional optical power, which may be supplied by a plus lens (spectacle or contact) or by
excessive use of the eye’s own focusing ability (accommodation).

Blood in the anterior chamber, such as following blunt trauma to the eyeball.


Intraocular Pressure
Fluid pressure inside the eye or the assessment of pressure inside the eye with a tonometer. Also
called tension.

The action or process of being turned inside out or folded back on itself to form a cavity or pouch.

Intraocular lens (IOL)
A plastic lens that may be surgically implanted to replace the eye’s natural lens.

Pigmented tissue lying behind the cornea that gives color to the eye (e.g., blue eyes) and controls
amount of light entering the eye by varying the size of the papillary opening.




Lacrimal Gland
The almond-shaped structure that produces tears, located at the upper outer region of the orbit,
above the eyeball.

LASIK (Laser-Assisted in Situ Keratomileusis)
A type of refractive surgery in which the cornea is reshaped to change its optical power. A disc of
cornea is raised as a flap, and then an Excimer laser is used to reshape the intrastromal bed,
producing surgical flattening of the cornea. LASIK is used for correcting myopia, hyperopia, and

Local Anesthesia
Anesthesia that affects a restricted area of the body.

Lucentis (ranibizumab) is made from a human antibody fragment. It works by keeping new blood
vessels from forming under the retina where they leak blood and fluid. This is known as the “wet
form” of macular degeneration.

Laser Photocoagulation
Laser photocoagulation uses the heat from a laser to seal or destroy abnormal, leaking blood
vessels in the retina. Laser photocoagulation may be used when treating diabetic retinopathy.

Lymphatic vessels
Lymph vessels (or lymphatic vessels) are thin walled, valved structures that carry lymph. As part
of the lymphatic system, lymph vessels are complementary to the cardiovascular system.


The small central area of the retina surrounding the fovea; area of acute central vision.

Myopia (nearsightedness)
A focusing defect in which the eye is overpowered. Light rays coming from a distant object are
brought to focus in front of the retina. Myopia generally requires a minor lens correction to
“weaken” the eye optically and permit clear distance vision.


The abnormal formation of new blood vessels, usually in or under the retina or on the iris surface.
Neovascularization may develop in diabetic retinopathy, blockage of the central retinal vein, or
macular degeneration.

Nonproliferative Retinopathy
In nonproliferative retinopathy (the most common form), capillaries in the back of the eye balloon
and form pouches. Nonproliferative retinopathy can move through three stages (mild, moderate,
and severe), as more and more blood vessels become blocked.


Outpatient Surgery
Outpatient surgery, also known as ambulatory surgery, same-day surgery or day surgery, is
surgery that does not require an overnight hospital stay.

A physician (Medical Doctor) specializing in diagnosis and treatment of refractive, medical and
surgical problems related to eye diseases and disorders.

An illuminated instrument for visualizing the interior of the eye (especially the fundus, the back
portion of the interior of the eyeball).

Optic Disc, Optic Nerve Head
The ocular end of the optic nerve that denotes the exit of retinal nerve fibers from the eye and
entrance of blood vessels to the eye.

Optic Neuritis
Optic neuritis is an inflammation of the optic nerve, the bundle of nerve fibers that transmits visual
information from your eye to your brain. Pain and temporary vision loss are common symptoms of
optic neuritis.

A professional who makes and adjusts optical aids, e.g., eyeglass lenses, from refraction
prescriptions supplied by an ophthalmologist or optometrist.

Optic Nerve
The largest sensory nerve of the eye; the optic nerve carries impulses for sight from the retina to
the brain.

A doctor of optometry (OD) specializing in vision problems, treating vision conditions with
spectacles, contact lenses, low vision aids and vision therapy, and prescribing medications for
certain eye diseases.

The discipline dealing with the diagnosis and treatment of defective eye coordination, binocular
vision, and functional amblyopia by non-medical and non-surgical methods, e.g., glasses, prisms,
and exercises.


Covering an amblyopic patientʼ s preferred eye to improve vision in the other eye.

A method of charting the extent of a stationary eyeʼ s field of vision with test objects of various
sizes and light intensities. Also aids in detection of damage to sensory visual pathways.

Peripheral Vision (Side Vision)
Vision elicited by stimuli falling on retinal areas distant from the macula.

Abnormal sensitivity to, and discomfort from, light. Photophobia may be associated with
excessive tearing, and often results from inflammation of the iris or cornea.

The use of ultrasonic vibration to shatter and break up a cataract, making it easier to remove.

Pink Eye
See conjunctivitis.

Refractive condition in which there is a diminished ability to focus on near objects arising from the
loss of elasticity of the crystalline lens, as occurs with aging. It usually becomes significant after
age 45.

Proliferative Retinopathy
A more serious form of retinopathy. In this form, the blood vessels are so damaged they close off.
In response, new blood vessels start growing in the retina. These new vessels are weak and can
leak blood, blocking vision, which is a condition called vitreous hemorrhage. The new blood
vessels can also cause scar tissue to grow. After the scar tissue shrinks, it can distort the retina
or pull it out of place, a condition called retinal detachment.

Pneumatic Retinopexy
An effective surgery for certain types of retinal detachments. It uses a bubble of gas to push the
retina against the wall of the eye, allowing fluid to be pumped out from beneath the retina. It is
usually an outpatient procedure done with local anesthesia.

An abnormal wedge-shaped growth on the bulbar conjunctiva that may gradually advance onto
the cornea and require surgical removal. Pterygium is often related to sun irritation.

A drooping of an upper eyelid. It may be congenital or caused by paralysis or weakness of the 3rd
cranial nerve or sympathetic nerves, or by excessive weight of the upper lids.

The variable-sized black circular opening in the center of the iris that regulates the amount of light
that enters the eye.



An eyeʼ s refractive error leading to prescribing of the best corrective lenses. A series of lenses in
graded powers are presented to determine which provide the sharpest, clearest vision.

Refractive Error
An optical defect in an unaccommodating eye; parallel light rays are not brought to a sharp focus
precisely on the retina, producing a blurred retinal image. This can be corrected by eyeglasses,
contact lenses, or refractive surgery.

Light sensitive nerve tissue in the eye that converts images from the eyeʼ s optical system into
electrical impulses that are sent along the optic nerve to the brain.

Retinal Detachment
The separation of the retina from the underlying pigment epithelium. Detachment disrupts visual
cell structure and thus markedly disturbs vision. It is almost always caused by a retinal tear and
often requires immediate surgical repair.

Refractive Power
The ability of a substance to refract light expressed quantitatively by either its index of refraction
or its refractivity.

Inflammation of the retina.

Retinopathy (Diabetic Retinopathy)
Diabetic retinopathy is a general term for all disorders of the retina caused by diabetes. There are
two major types of retinopathy: nonproliferative and proliferative.

An RNA molecule capable of acting as an enzyme.

A light-sensitive, specialized retinal receptor cell that works at low light levels (night vision). A
normal retina contains 150 million rods.


Schlemmʼs Canal
A circular channel deep in corneoscleral junction (limbus) that carries aqueous fluid from the
anterior chamber of the eye to the bloodstream.

The opaque, fibrous, protective outer layer of the eye (“white of the eye”) that is directly
continuous with the cornea in front and with the sheath covering the optic nerve behind.

Scleral Buckle
One of several ophthalmologic procedures that can be used to repair a retinal detachment.
Retinal detachments are usually caused by retinal tears, and a scleral buckle can be used to
close the retinal break.

Snellen Chart
The test chart used for assessing visual acuity. It contains rows of letters, numbers, or symbols in
standardized graded sizes, with a designated distance at which each row should be legible to a
normal eye. The patient is usually tested at 20 feet.

An abnormal alignment of the eyes; the condition of having a squint.

An acute pustular infection of the oil glands of Zeis, located in an eyelash follicle at the eyelid

The layer immediately under the epithelium.


The measurement of intraocular pressure.

A general term for a supporting or anchoring strand of connective tissue. Trabeculae form a mesh
located near the cornea and iris that functions to drain the aqueous humor from the eye into the

A surgical procedure that removes part of the trabeculum in the eye to relieve pressure caused by

Eyeglass lens that incorporates three lenses of different powers. The main portion is usually
focused for distance (20 feet), the center segment for about 2 feet, and the lower segment for
near distances (14 inches).

20/20 Vision
Normal visual acuity. The upper number is the standard distance (20 feet) between an eye being
tested and the eye chart; the lower number indicates that a tested eye can see the same small
standard-sized letters or symbols as a normal eye at 20 feet.


Pigmented layers of the eye (iris, ciliary body, choroid) that contain most of the intraocular blood

An inflammation of the uvea, the middle layer of the eye. The uvea consists of the iris, choroid
and ciliary body. The choroid is sandwiched between the retina and the white of the eye (sclera),
and it provides blood flow to the deep layers of the retina. The most common type of uveitis is an
inflammation of the iris called iritis (anterior uveitis).


Visual Acuity
Assessment of the eyeʼ s ability to distinguish object details and shape, using the smallest
identifiable object that can be seen at a specified distance (usually 20 feet or 16 inches).

Visual Field
The full extent of the area visible to an eye that is fixating straight ahead.

The surgical removal of the vitreous (transparent gel that fills the eye from the iris to the retina).

Vitreous (Vitreous Humor)
The transparent, colorless gelatinous mass that fills the rear two-thirds of the eyeball, between
the lens and the retina.

Vitreous Detachment
A separation of vitreous gel from the retinal surface. Usually innocuous, vitreous detachment can
cause retinal tears, which may lead to retinal detachment. It frequently occurs with aging as the
vitreous liquefies, or in some disease states, e.g. diabetes and high myopia.




YAG Laser (Yttrium Aluminum Garnet)
A laser that produces a short pulsed, high-energy light beam to cut, perforate, or fragment tissues.


Zeis Gland
Any of the numerous sebaceous glands opening into the follicles of the eyelashes.
Radially arranged fibers that suspend the lens from the ciliary body and hold it in position.


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