| Astigmatism |
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A condition in which the surface of the cornea is not spherical; causes a blurred image to be received at the retina. |
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| Binocular Vision |
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The blending of the separate images seen by each eye into a single image; allows images to be seen with depth. |
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| Blind Spot |
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(1) A small area of the retina where the optic nerve enters the eye; occurs normally in all eyes.
(2) Any gap in the visual field corresponding to and area of the retina where no visual cells are present; associates with eye disease.
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| Contrast Sensitivity |
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The ability to perceive differences between an object and its background. |
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| Cornea |
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The outer, transparent, dome-like structure that covers the iris, pupil, and anterior chamber; part of the eye's focusing system. |
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| Dilation |
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A process by which the pupil is temporarily enlarged with special eye drops (mydriatic); allows the eye care specialist to better view the inside of the eye. |
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| Fundus |
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The interior lining of the eyeball, including the retina, optic disc, and macula; portion of the inner eye that can be seen during an eye examination by looking through the pupil. |
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| Hyperopia |
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Farsightedness; ability to see distant object more clearly than close object; may be corrected with glasses or contact lenses. |
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| Iris |
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The colored ring of tissue suspended behind the cornea and immediately in front of the lens; regulates the amount of light entering the eye by adjusting the size of the pupil. |
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| Legal Blindness |
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In the U.S., (1) visual acuity 20/200 or worse in the better eye with corrective lenses (20/200 means that a person must be at least 20 feet from an eye chart to see what a person with normal vision can see at 200 feet) or (2) visual field restricted to 20 degrees diameter or less (tunnel vision) in the better eye. NOTE: These criteria are used to determine eligibility for government disability benefits and do not necessarily indicate a person's ability to function. |
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| Lens |
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The transparent, double convex (outward curve on both sides) structure suspended between the aqueous and vitreous; helps to focus light on the retina. |
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| Low Vision |
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Visual loss that cannot be corrected with eyeglasses or contact lenses and interferes with daily living activities. |
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| Myopia |
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Nearsightedness; ability to see close objects more clearly that distant objects; may be corrected with glasses or contact lenses. |
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| Peripheral Vision |
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Side vision; ability to see objects and movement outside the direct line of vision. |
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| Presbyopia |
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The gradual loss of the eye's ability to change focus (accommodation) for seeing near objects caused by the lens becoming less elastic; associated with aging; occurs in almost all people over age 45. |
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| Pupil |
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The adjustable opening at the center of the iris that allows varying amounts of light to enter the eye. |
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| Refraction |
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A test to determine the best eyeglasses or contact lenses to correct a refractive error (myopia, hyperopia, or astigmatism) |
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| Retina |
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The light-sensitive layer of tissue that lines the back of the eyeball; sends visual messages through the optic nerve to the brain. |
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| Tonometry |
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The standard to determine the fluid pressure inside the eye (intraocular pressure). |
| Visual Acuity |
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The ability to distinguish details and shapes of objects; also called central vision. |
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| Visual Field |
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The entire area that can be seen when the eye is forward, including peripheral vision. |
