| ACCOMMODATION | The ability of the eye to increase its power to keep a clear image as objects are moved closer; it occrus through a process that causes the lens to "round up." |
| ANTERIOR CHAMBER | The space in front of the iris and behind the cornea. |
| AQUEOUS HUMOR, AQUEOUS FLUID (A-kwe-us) | Clear, watery fluid that fills the space between the surface of the cornea and the front surface of the vitreous, bathing the lens; nourishes the lens, iris and the cornea; maintains intraocular pressure. |
| ASTIGMATISM (uh-STIG-muh-tizm) | A condition in which the surface of the cornea is not spherical, which prevents the formation of a sharp image focus on the retina. |
| BINOCULAR VISION | The blending of the separate images seen by each eye into a single image; allows images to be seen with depth. |
| 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. |
| CENTRAL RETINAL ARTERY | The blood vessel that carries blood into eye; supplies nutrition to the retina. |
| CENTRAL RETINAL VEIN | The blood vessel that carries blood from the retina. |
| CENTRAL VISION | See VISUAL ACUITY. |
| CHOROID (KOR-oyd) | The layer filled with blood vessels that nourishes outer layers of the retina; part of the uvea. |
| CONES, CONE CELLS | One type of specialized light-sensitive cells (photoreceptors) in the retina that provide sharp central vision and color vision. Also see RODS. |
| CONJUNCTIVA (KAHN-junk-TY-vuh) | The thin, moist tissue (membrane) that lines the inner surfaces of the eyelids and the outer surface of the eyeball except the cornea. |
| CORNEA (KOR-nee-uh) | Transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye's optical power. |
| DIABETIC RETINOPATHY | Spectrum of retinal changes accompanying long-standing diabetes mellitus; early stage is background retinopathy; may advance to proliferative retinopathy, which includes the growth of abnormal new blood vessels (neovascularization) and fibrous tissue. |
| DILATION | A process by which the pupil is temporarily enlarged with special eye drops (mydriatics); allows the eye care specialist to better view the inside of the eye. |
| FLOATERS | Particles that float in the vitreous and cast shadows on the retina; seen as spots, cobwebs, spiders; Occurs normally with aging or with vitreous detachment, retinal tears, or inflammation. |
| FLUORESCEIN ANGIOGRAPHY (FLOR-uh-seen an-jee-AHG-ruh-fee) | A test to examine blood vessels in the retina, choroid and iris. A special dye is injected into a vein in the arm and pictures are taken as the dye passes through blood vessels in the eye. |
| FOVEA (FOH-vee-uh) | The central part of the macula that provides the sharpest vision. |
| GLAUCOMA | Group of diseases characterized by increased intraocular pressure resulting in damage to the optic nerve and retinal nerve fibers. A common cause of preventable vision loss. May be treated by prescription drugs or surgery. . |
| HYPEROPIA (hy-pur-OH-pee-uh) | Farsightedness; ability to see distant objects more clearly than close objects; may be corrected with glasses or contact lenses. |
| INTRAOCULAR PRESSURE (IOP) | Pressure of the fluid inside the eye; also called tension. |
| IRIS | The colored ring of tissue suspended behind the cornea and immediately in front of the lens; gives color to the eye and controls the amount of light entering the eye by adjusting the size of the pupil. |
| LACRIMAL GLAND (LAK-rih-mul) | The small almond-shaped structure that produces tears; located just above the outer corner of the eye. |
| LEGAL BLINDNESS | In the U.S.,
(1) visual acuity of 20/200 or worse in the better eye with corrective lenses (20/200 means that a person must be at 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. |
| LENS | The transparent, double convex (outward curve on both sides) tissue that helps bring rays of light to focus on the retina. |
| LOW VISION | Visual loss that cannot be corrected with eyeglasses or contact lenses and interferes with daily living activities; usually used to indication vision of less than 20/200. |
| MACULA (MAK-yoo-luh) | The small, sensitive area of the central retina; provides vision for fine work and reading. |
| OPTICIAN | Professional who makes and adjusts vision aids, such as eyeglass lenses from refraction prescriptions supplied by an opthalmologist or optometrist. |
| OPTIC DISC/OPTIC NERVE HEAD | The circular area (disc) where the optic nerve connects to the retina. |
| OPTIC NERVE | Largest sensory nerve of the eye; carries impulses for sight from the retina to the brain. |
| OPTOMETRIST | 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. |
| PERIPHERAL VISION (per-IF-ur-al) | Side vision; ability to see objects and movement outside of the direct line of vision. |
| PHOTOPHOBIA | Abnormal sensitivity to, and discomfort from, light. May be associated with excessive tearing. Often due to inflammation of the iris or cornea. |
| PRESBYOPIA (prez-bee-OH-pee-uh) | 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. |
| PUPIL | The adjustable opening at the center of the iris that allows varying amounts of light to enter the eye. |
| REFRACTION | A test to determine the best eyeglasses or contact lenses to correct a refractive error (myopia, hyperopia, or astigmatism). |
| RETINA (RET-in-nuh) | The light-sensitive layer of tissue that lines the back of the eyeball; sends visual messages through the optic nerve to the brain. |
| RETINAL PIGMENT EPITHELIUM (RPE) (ep-ih-THEE-lee-um) | The pigment cell layer that nourishes the retinal cells; located just outside the retina and attached to the choroid. |
| RODS, ROD CELLS | One type of specialized light-sensitive cells (photoreceptors) in the retina that provide side vision and the ability to see objects in dim light (night vision). Also see CONES. |
| SCHLEMM'S CANAL | The passageway for the aqueous fluid to leave the eye and enter the bloodstream. |
| SCLERA (SKLEH-ruh) | The protective outer layer of the eye ("white of the eye"); with the cornea, it protects the entire eyeball. |
| TRABECULAR MESHWORK (truh-BEC-yoo-lur) | The spongy, mesh-like tissue near the front of the eye that allows the aqueous fluid (humor) to flow to Schlemm's canal then out of the eye through ocular veins. |
| 20/20 | Normal visual acuity. Upper number is the standard distance (20 ft.) between an eye being tested and the eye chart; lower number indicates that the tested eye can see the same small standard-sized letters or symbols as a normal eye at 20 feet. |
| UVEA, UVEAL TRACT (YOO-vee-uh) | Pigmented layers of the eye (iris, ciliary body, choroid) that contain most of the intraocular blood vessels. |
| VISUAL ACUITY | The ability to distinguish details and shapes of objects; also called central vision. |
| VISUAL FIELD | The entire area that can be seen when the eye is looking straight ahead, including peripheral vision. |
| VITREOUS (VIT-ree-us) | The transparent, colorless mass of gel that lies behind lens and in front of retina. |
