Glossary: The Aging Eye Preventing And Treating Eye Disease

Content provided by the Faculty of the Harvard Medical School

Glossary

anterior chamber: The space behind the cornea and in front of the iris; it is filled with aqueous humor.

aqueous humor: The watery fluid that nourishes the eye and fills the anterior and posterior chambers.

astigmatism: A refractive error characterized by irregular curvature of the cornea or lens, causing distorted images.

cones: Specialized cells in the retina that are sensitive to color and light; they are more active in light than in the dark, provide sharp vision, and are abundant in the macular area of the retina.

conjunctiva: The transparent membrane that lines the eyelid and covers the front portion of the sclera.

cornea: The curved, transparent dome of tissue at the front of the eye, through which light first passes on its way into the eye.

crystalline lens: A flexible, transparent structure directly behind the iris that focuses rays of light onto the retina.

drusen: Tiny yellow deposits that form beneath the macula and may indicate early stages of age-related macular degeneration.

fluorescein angiography: A diagnostic test that photographs blood vessels in the retina after the intravenous injection of a special dye.

fovea: A pit-like depression in the middle of the macula.

hyperopia: An optical error in which light rays reach the retina before converging at a focus point; commonly known as farsightedness.

intraocular lens: A small artificial lens permanently fixed inside the eye to replace the natural lens during cataract surgery.

iris: The colored ring in front of the lens that controls the size of the pupil and how much light enters the eye.

lacrimal gland: The gland that produces tears; located in the upper, outer section of the eye's orbit.

macula: The area of the retina packed with cones, responsible for sharp central vision.

miotic: A type of eye drop that constricts the pupil; used to treat glaucoma.

mydriatic: A type of drug that dilates the pupil.

myopia: An optical error in which light rays meet and focus before reaching the retina; also known as nearsightedness.

ophthalmoscope: An instrument with a light and mirrors for examining the deep interior of the eye.

optic nerve: A "cable" that emanates from the back of the eye, consisting of specialized nerve fibers that transmit visual impulses to the brain.

orbit: The bony socket that surrounds the eyeball.

peripheral vision: Side vision, or what the eye perceives outside the direct line of vision.

posterior chamber: The area behind the iris and in front of the lens that is filled with aqueous humor.

retina: The innermost layer of the eye, consisting of specialized cells and lining nearly three-quarters of the back of the eye; it converts light energy to electrical energy and sends visual images to the brain via the optic nerve.

rods: Light-sensitive cells in the retina that respond best in darkness and dim light.

sclera: The white of the eye; a tough, protective coating of collagen and elastic tissue that, with the cornea, makes up the outer layer of the eyeball.

slit lamp: An instrument that magnifies internal structures of the eye with the aid of a slit beam of light. Also called a biomicroscope.

tonometry: A glaucoma screening test that measures pressure inside the eye.

visual acuity: The eye's ability to see sharply, usually measured in comparison with what a normal eye would see from 20 feet.

visual field: The scope of what the eye sees; includes central and peripheral vision.

vitreous humor: The clear, gel-like substance that fills the space behind the lens and supports the shape of the rear portion of the eye.

Last updated:	June 19, 2007