| ACCOMMODATION | The ability of the eye to change its focus from distant to near objects; process achieved by the lens changing its shape. |
| ANTERIOR CHAMBER | The space in front of the iris and behind the cornea. |
| AQUEOUS HUMOR, AQUEOUS FLUID
(A-kwe-us) |
Clear, watery fluid that flows between and nourishes the lens and the cornea; secreted by the ciliary processes. |
| ASTIGMATISM (uh-STIG-muh-tizm) |
A condition in which the surface of the cornea is not spherical; causes a blurred image to be received at 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 | (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 an area of the retina where no visual cells are present; associated with eye disease. |
| 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 the retina; part of the uvea. |
| CILIARY MUSCLES | The muscles that relax the zonules to enable the lens to change shape for focusing. |
| CILIARY PROCESSES | The extensions or projections of the ciliary body that secrete aqueous humor. |
| 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 sclera. |
| CONTRAST SENSITIVITY | The ability to perceive differences between an object and its background. |
| The outer, transparent, dome-like structure that covers the iris, pupil, and anterior chamber; part of eye's focusing system. |
| DILATION | 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. |
| DRUSEN | Tiny yellow or white deposits in the retina or optic nerve head. |
| 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. |
| FUNDUS | 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. |
| 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; normal IOP varies among individuals. |
| IRIS | 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. |
| 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) structure suspended between the aqueous and vitreous; helps to focus light on the retina. |
| LOW VISION | Visual loss that cannot be corrected with eyeglasses or contact lenses and interferes with daily living activities. |
| MACULA (MAK-yoo-luh) |
The small, sensitive area of the central retina; provides vision for fine work and reading. |
| MYOPIA (my-OH-pee-uh) |
Nearsightedness; ability to see close objects more clearly than distant objects; may be corrected with glasses or contact lenses. |
| OPTIC CUP | The white, cup-like area in the center of the optic disc. |
| OPTIC DISC/OPTIC NERVE HEAD | The circular area (disc) where the optic nerve connects to the retina. |
| OPTIC NERVE | The bundle of over one million nerve fibers that carry visual messages from the retina to the brain. |
| PERIPHERAL VISION (per-IF-ur-al) |
Side vision; ability to see objects and movement outside of the direct line of vision. |
| POSTERIOR CHAMBER | The space between the back of the iris and the front face of the vitreous; filled with aqueous fluid. |
| 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. |
| SCLERA (SKLEH-ruh) |
The tough, white, outer layer (coat) of the eyeball; with the cornea, it protects the entire eyeball. |
| TONOMETRY | The standard to determine the fluid pressure inside the eye (intraocular pressure). |
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