A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z

A

Abduction: The rotation of an eye away from the midline, or centerpoint of vision. Also the diverging of the eyes away from each other.

Abscess: A localized collection of pus; an infected pocket of tissue

Accommodation: The ability of the eye to focus and maintain a clear image as objects are moved closer. The ciliary muscles of the eye contract and the zonules relax, causing the flexible crystalline lens to "round up" and increase its optical power. When a person ages and begins to lose accommodation, it is referred to as presbyopia .

Achromasia: The absence of pigment; albinism; total color blindness.

Achromatism: The condition of being totally color-blind or color-less.

Acorea: The absence of the pupil of the eye.

Acuity: Visual ACUITY refers to a standard that represents the clearness or sharpness in vision or sight. Visual acuity may be referred to as the "resolution" in vision.

The most common standard for measuring visual acuity is Snellin Acuity. The Snellin standard is usually used to define "distance" visual acuity. Under the Snellin standard the object is placed 20 feet from the observer. The measurement is always in reference to this 20 foot distance. As an example, consider a person who is said to have 20/40 visual acuity. 20/40 means that the person being tested had to move up to 20 feet from the object in order to see a letter which was actually placed 40 feet from the observer.

The test objects that are traditionally used to subjectively test visual acuity are: Capitol letters, Rotating "C"s, Tumbling "E"s (for children).

Another standard for measuring visual acuity is Jaeger acuity. This is defined in terms of a metric reference. The jaeger standard is most often used in measuring "near point" vision, rather than distance vision.

Acyanopsia: The inability to distinguish blue tints.

Adduction: The rotation of the eye toward the midline of the body (in the direction of the nose).

Adenoma: A benign tumor originating from, or resembling, glandular epithelium. It is of endocrine or exocrine origin.

Adie's Pupil: Adie's Pupil, or Adie Syndrome is a rare neurological disorder affecting the pupil of the eye. It is a condition in which the pupil does not react normally to bright light due to impaired nerve function. Adie's Pupil usually does not interfere substantially with normal vision.

Adnexa: The appendages or adjoining anatomical parts of the eye (eyelids, conjunctiva, extraocular muscles and glands of the eye).

After-Cataract, Secondary cataract: An after-cataract, or secondary cataract, is one that forms following cataract removal surgery. Typically it occurs when a piece of the cataract remains or when scar tissue has formed an opacity.

Agnosia, Spatial: The inability to orientate one's self in space, usually accompanied by visual agnosia, due to a disturbance in the brain.

Allergic Lid Edema: Allergic Lid Edema refers to the eyelid swelling that is typically the result of an allergic reaction to external irritants.

Amaurosis Fugax: The temporary loss of vision in one eye without visible ocular lesions. Amaurosis Fugax may be a sign of a transient ischemic attack (TIA) or can be indicative of an impending stroke.

Ambiocular: A term meaning "with both eyes together", with both eyes in sync.

Amblyopia, Lazy Eye: AMBLYOPIA is commonly referred to as "lazy eye". Amblyopia is a term used to denote poor vision in an eye without any discoverable pathologic condition causing it. Sometimes it is called "Amblyopia ex anopsia"or amblyopia from disuse. It has been likened to the phrase "If you don't use it, you lose it". If vision is less than that of the other eye, it may be clinically diagnosed as Amblyopia.It is a condition in which visual acuity is reduced and not completely correctable by refractive methods.

Ametropia: An imperfection in the refractive power of the eye, such as nearsightedness, farsightedness, or astigmatism.

Amsler grid: A chart featuring horizontal and vertical lines used to test vision.This test is extremely useful in diagnosing macular degeneration. Click Here to view the Amsler Grid.

Anatropia: The persistent and abnormal upturning of the visual axes above the horizontal plane; turning upward.

Angioma: A tumor composed of lympathic or blood vessels. Forms include Angioma pigmentosum atrophikum, and angiomatosis (Sturge-Weber disease).

Anisocoria: A condition in which each pupil is of different size. Simple aniscoria occurs in 20% of otherwise normal individuals and is not a problem. The pupils can vary by a size of 0.3 and 0.5 millimeters.

Anisometropia: A difference in refractive error of the eyes.

Ankyloblepharon: An adhesion between the margins of the eyelids.

Anophthalmia: No eyeball; also called anophthalmos.

Anterior Chamber: The anterior chamber is the fluid-filled space inside the eye between the iris and the endothelium.

Anterior Chamber Hemorrhage: A rupture in the anterior chamber of the eye.

Anti-Reflection Coating: Special anti-reflective coatings are much like those used for fine camera lenses. These coatings are particularly effective for reducing eye fatigue for computer operators and anyone driving at night. And, of course, anti-reflection coatings on lenses enhance appearance by removing all distracting reflections.

Aphakia, Aphakic: A term meaning the natural lens is missing. Absence of a lens is often the result of surgical procedures such as cataract removal but also can be injury-related or more rarely, due to a congenital defect. A person who has had cataract surgery without a lens implant is said to be "aphakic".

Aqueous flare: The abnormal visibility of a beam of light as it passes through anterior chamber; due to increase in protein content of aqueous humor.

Aqueous Humor: The clear fluid inside the eye orbit that, under proper level and pressure, keeps the rounded shape to the cornea. This fluid is produced by the ciliary body and drains through the trabecular meshwork. If this fluid doesn't drain properly, pressure builds within the eye and presses on the optic nerve. This condition is called glaucoma.

Arcus Senilis: A hazy ring at the edge of the cornea where the iris meets the white of the eye but does not impair vision.

Artery Occlusion: Retinal artery occlusion occurs when the central retinal artery or one of the arteries that branch off of it becomes blocked by a tiny clot in the blood stream. The blockage decreases the oxygen supply to the area of the retina nourished by the affected artery, causing permanent vision loss. Different types of occlusion include a central retinal artery occlusion and a branch retinal artery occlusion.

Artificial Silicon Retina, Macular Degeneration: A new device designed to treat Macular Degeneration and Retinitis Pigmentosa has been developed and is under review. Artificial Silicon Retinas™ (ASR) are 2 mm silicon chips about the thickness of paper. They were first implanted in the retinas of three people in 2000. Each chip has 3,500 microscopic solar cells, each with an electrode designed to stimulate remaining retinal cells from underneath the retina in a pattern resembling the light images focused on the chip. The chips are completely self contained and receive their power from the light that enters the eye. They require no wires or batteries.

A-Scan: Provides two functions: one is to calculate the axial length (AL) of the eye and the other is to take that axial length along with a keratometer measurement and then calculate the best projected power of the proposed IOL.

The method by which the A-Scan calculates the AL is like radar. A sound impulse is echoed off the back of the eye and the time is takes for the echo to return to the probe is converted into the AL with an oscilloscope-type display.

Aspheric Lens: A lens that resembles an ellipse, parabola, or other conic section rather than a sphere. It can be designed to improve the fit and comfort of a lens by paralleling the cornea more closely.

Asteroid Hyalosis: Spherical and stellate opacities in the vitreous; made of calcium-lipid combinations.

Astigmatism: The result of having a cornea that is irregular in shape. The cornea is normally round. An astigmatic cornea is oblong or "football" shaped, resulting in a condition that generally causes eyestrain, headaches and blurry vision. Astigmatism is often associated with nearsightedness and farsightedness.

The simple act of reading often creates headaches and eyestrain, since the image is never completely clear. The individual may have to re-read the word several times.

Axenfeld-Rieger Syndrome: A rare, congenital ocular disorder in which glaucoma may be present along with a flattened nose and/or developmental defects of the teeth (fewer teeth than normal) and facial bones . There may be some atrophy or lack of coloring of the iris, pituitary problems, cardiac disease.

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