Eye Dictionary

Eye Dictionary - A

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aberration: Blurred or distorted image quality that results from inherent physical properties (shape, curvature, density) of an optical device such as a lens or prism.
ablate, ablation: To remove by cutting. The surgical removal of any part of the body.
absorption spectrum: The relationship between wavelengths of light striking a pigment and how strongly the light is absorbed.
accommodation: The ability of the eye to change its focus from distant to near objects as well as from near to distance objects. This process is achieved by the crystalline lens changing its shape.
achromatopsia: Congenital absence of the ability to see colors. Caused by absence or defects in light- sensitive retinal receptor cells (cones) that provide sharp visual acuity and color discrimination.
See Color Blindness in Eye Care Encyclopedia.
add: Amount of plus (+) refractive power required for near use (over eyeglass correction for distance).
adjustable bridge: Part of the eyeglass frame that includes nose pads that can be adjusted for fit and comfort.
afterimage: A sensation of seing an object that is no longer in your sight. Also called aftersensation, aftervision.
age-related macular degeneration: Degeneration of the photoreceptors in the macula or central region of the retina. This area of the retina is responsible for central vision, used for reading, seeing faces, and so on. Often associated with aging.
See Age-Related Macular Degeneration in Eye Care Encyclopedia.
See Basic Anatomy.
AIDS-related eye disorders: Anyone who is HIV positive should have regular eye examinations by an ophthalmologist, especially if their T-cell count falls under 250 or if vision changes are obvious. The most common eye problem from AIDS is called Cotton Wool Spots and is not a serious threat to vision. Tiny white spots on the retina, caused by bleeding, are called Cotton Wool Spots because of how they look. A more serious problem is an eye infection caused by cytomegalovirus (CMV) which can permanently impair vision. Symptoms include flashing spots or “spiderwebs,” flashing lights, and blind spots or blurred vision. Other AIDS-related eye disorders include red eye, shingles, detached retina and Kaposi’s sarcoma, a slow growing tumor on the eyelid or spot on the white of the eye.
AK: Acronym for Astigmatic Keratotomy. A surgical procedure used to correct moderate cases of astigmatism. Often performed at the same time as the Radial Keratotomy (RK) procedure for correcting nearsightedness. The procedures are somewhat similar, differing primarily in the pattern of incisions made in the outer periphery of the cornea in order to change its shape to the curvature needed to correct the refractive problem. Both AK and RK have been largely replaced by newer refractive surgery procedures.
See Refractive Surgery in Eye Care Encyclopedia.
ALK: Automated Lamellar Keratoplasty. A refractive eye surgery procedure that uses an instrument named a microkeratome to lift a flap of corneal material and to sculpt the underlying corneal tissue. Has been used successfully in correcting relatively high degrees of nearsightedness and some cases of farsightedness, but has been largely replaced by LASIK and other laser procedures that offer greater accuracy.
See Refractive Surgery in Eye Care Encyclopedia.
allergies of the eye: Allergic reactions triggered by the body’s immune system to protect eyes from injury. Ocular allergies can be seasonal, such as those caused by pollens, or caused by bacterias, food sensitivities, cosmetics, fabrics, soaps and other substances. Visible symptoms of eye allergies may include swelling, hives, itching, watering, eye pain and sensitivity to light.
allyl resin plastic lens: The lightest of all vision-correction lenses. But they are thicker than other plastic lenses, are less scratch resistant, and do not block as much ultraviolet light as polycarbonate and glass lenses.
aluminum: Eyeglass frame material that is lightweight, yet difficult to solder or weld, limiting its adaptability to different designs.
amacrine cell: A type of neuron seen in the retina.
amblyopia: Also called lazy eye, this is a condition of decreased vision in one or both eyes that occurs without detectable structural abnormalities or disease in the eye or visual pathways. Best corrected vision is usually less than 20/20.
AMD: Acronym for age-related macular degeneration. A degeneration of the photoreceptors in the macula or central region of the retina. This area of the retina is responsible for central vision, for reading, seeing faces, and so on. Often associated with aging.
See Age-related Macular Degeneration in Eye Care Encyclopedia.
Amsler grid: Home eye test featuring equally spaced horizontal and vertical lines in a grid pattern. Used for determining the presence of macular degeneration and other defects that affect central vision.
See Age-related Macular Degeneration in Eye Care Encyclopedia.
aneurysm: Weakness of the wall of an artery causing abnormal enlargement or bulge. Tiny aneurysms may occur in the veins of the retina of the eye as a complication of diabetes.
angiography: Test used to examine blood vessels in the retina, choroid and iris of the eye.
See also Fluorescein Angiography
angioma: Benign tumor consisting of small blood vessels. Can be located anywhere on the body and is not dangerous or contagious. Can affect eye with tumors beneath or on top of the retina, which may lead to blood leakage and possible retinal detachment.
See also Von Hippels Angioma
aniridia: A birth defect in which a child is born without an iris, so there is no way to control the amount of light that enters the eye. The only treatment is to use colored eye lenses to reduce the amount of light entering the eye.
anisometropia: A condition that occurs when each of a person's eyes have a different refractive power.
ANSI 287.1: The American National Standards Institute’s guidelines for Occupational and Educational Eye and Face Protection. ANSI 287.1 ensures the quality and safety level of eye protection.
anterior: Front or forward area of an object.
anterior segment: Front third of eyeball, including the cornea, anterior chamber, iris and ciliary body.
anterior capsulotomy: Cataract surgery technique used to make a round opening in the front (anterior) of the capsule, which encases the eye’s natural lens.
antioxidants: General label for vitamins, enzymes and minerals that may help prevent damage to the body caused by oxygen free radicals, harmful by-products produced during normal metabolism. Some evidence suggests that antioxidants may be beneficial for arthritis, cancer, blood vessel disorders, inflammation, allergies, heart disease, blood pressure, gum disease, eye problems, lung and nervous system problems and skin care. Many over-the- counter vitamins now contain antioxidants, including some formulated especially for the eye. Commonly recognized antioxidants include vitamins A, C and E, and yellow-colored carotenoids such as beta-carotene.
anti-reflective coatings (A-R coatings): Metallic oxide coatings that are vacuum-applied to the eyeglass lens surface to reduce reflections from the front lens surface and eliminate reflections from the back. This reduced amount of reflection enhances the appearance of the glasses and allows more light to pass through the lenses, which can improve vision in low-light situations. Anti-reflective coatings also provide some protection from scratching.
aphakia: Absence of the eye’s natural crystalline lens, usually after cataract extraction.
apparent motion: An optical illusion in which stationary objects viewed in quick succession or in relation to moving objects appear to be in motion. Also called apparent movement.
A-Scan: Type of ultrasound device that emits very high frequency waves that are reflected by the ocular structures and converted into electrical impulses. Used for differentiating normal and abnormal eye tissue or for measuring length of eyeball.
aspheric lens: Vision-correction lens material that is thin and light, especially when combined with high index materials. Aspherics have curves that are nonspherical and change gradually from the center to the outside of the lens. Aspherics are now available in single vision, bifocal, and progressive addition designs.
Astigmatic Keratotomy (AK): Surgical procedure used to correct moderate cases of astigmatism. Often performed at the same time as the Radial Keratotomy (RK) procedure for correcting nearsightedness. The procedures are somewhat similar, differing primarily in the pattern of incisions made in the outer periphery of the cornea in order to change its shape to the curvature needed to correct the refractive problem. Both AK and RK have been largely replaced by newer refractive surgery procedures.
See Refractive Surgery in Eye Care Encyclopedia.
astigmatism: Uneven curvature of the cornea in which refractive light rays are bent out of focus resulting in distorted vision. Those people with astigmatism are usually born with the disorder and it does not worsen with age. Often occurs in conjunction with nearsightedness or farsightedness.
See General Eye Care in Free Eye Tests.
See Cornea in Basic Anatomy.
asthenopia: The term for eye strain.
antireflective (AR) coating: Thin layer(s) applied to an eyeglass lens to decrease glare and surface reflections.
See Prescription Eyeglasses in Eye Care Encyclopedia.
Automated Lamellar Keratoplasty (ALK) (index to Automated Lamellar Keratoplasty): Refractive eye surgery procedure that uses an instrument known as a microkeratome to lift a flap of corneal material and to sculpt the underlying corneal tissue. Has been used successfully in correcting relatively high degrees of nearsightedness and some cases of farsightedness, but has been largely replaced by LASIK and other laser procedures that offer greater accuracy.
automatic keratometer: Instrument used to measure curvature of the front surface of the cornea.
automatic lens meter
automatic lensometer: Instrument used by an eyecare professional to determine the refractive power of an eyeglass or contact lens.
automatic refractor: Electro mechanical device that provides an “objective” measurement of an eye’s refractive error.
automatic perimeter: A computer-driven instrument used during an eye examination to plot possible defects in the field of vision (visual field). During the procedure, points of light are projected to various spots inside a large “globe” while the patient indicates whether or not the lights can be seen.