Eye Library


9939696_mConfused about what you might have heard at your appointment, have questions about certain terminology the doctor used, or just interested in eye health?  Check out this list of commonly used terms below for more information, or feel free to give us a call if you still have questions!

amblyopia (“lazy eye”) – Decreased vision in one or both eyes without detectable anatomic damage in the eye or visual pathways. Usually uncorrectable by eyeglasses or contact lenses.

anterior chamber – Fluid-filled space inside the eye between the iris and the innermost corneal surface (endothelium).

astigmatism  Optical defect in which refractive power is not uniform in all directions (meridians). Light rays entering the eye are bent unequally by different meridians, which prevents formation of a sharp image focus on the retina. Slight uncorrected astigmatism may not cause symptoms, but a large amount may result in significant blurring and headache.

bifocals – Eyeglasses that incorporate two different powers in each lens, usually for near and distance corrections.

cataract – Opacity or cloudiness of the crystalline lens, which may prevent a clear image from forming on the retina. Surgical removal of the lens may be necessary if visual loss becomes significant, with lost optical power replaced with an intraocular lens, contact lens, or aphakic spectacles. May be congenital or caused by trauma, disease, or age.

chalazion – Inflammed lump in a meibomian gland (in the eyelid). Inflammation usually subsides, but may need surgical removal. Sometimes called an internal hordeolum.

conjunctivitis (pink eye) – Inflammation of the conjunctiva. Characterized by discharge, grittiness, redness and swelling. Usually viral in origin, but may be bacterial or allergic; may be contagious.

convergence – Inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision as an object approaches.

cornea – Transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye’s optical power.

cross-eyes (esotropia) – Eye misalignment in which one eye deviates inward (toward nose) while the other fixates normally. 

dilated pupil – Enlarged pupil, resulting from contraction of the dilator muscle or relaxation of the iris sphincter. Occurs normally in dim illumination, or may be produced by certain drugs (mydriatics, cycloplegics) or result from blunt trauma.

exotropia – Eye misalignment in which one eye deviates outward (away from nose) while the other fixates normally.

farsightedness (hyperopia) – Focusing defect in which an eye is underpowered. Thus light rays coming from a distant object strike the retina before coming to sharp focus, blurring vision. Corrected with additional optical power, which may be supplied by a plus lens (spectacle or contact) or by excessive use of the eye’s own focusing ability (accommodation).

floaters – Particles that float in the vitreous and cast shadows on the retina; seen as spots, cobwebs, spiders, etc. Occurs normally with aging or with vitreous detachment, retinal tears, or inflammation.

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.

hyphema – Blood in the anterior chamber, such as following blunt trauma to the eyeball.

intraocular pressure – 1. Fluid pressure inside the eye. 2. The assessment of pressure inside the eye with a tonometer. Also called tension.

iris – Pigmented tissue lying behind the cornea that gives color to the eye (e.g., blue eyes) and controls amount of light entering the eye by varying the size of the pupillary opening.

macula – Small central area of the retina surrounding the fovea; area of acute central vision.

nearsightedness (myopia) – Focusing defect in which the eye is overpowered. Light rays coming from a distant object are brought to focus in front of the retina. Requires a minus lens correction to “weaken” the eye optically and permit clear distance vision.

nystagmus – Involuntary, rhythmic side-to-side or up and down (oscillating) eye movements that are faster in one direction than the other.

optic nerve – Largest sensory nerve of the eye; carries impulses for sight from the retina to the brain.

patching – Covering an amblyopic patient’s preferred eye, to improve vision in the other eye.

ptosis – Drooping of upper eyelid. May be congenital or caused by paralysis or weakness of the 3rd cranial nerve or sympathetic nerves, or by excessive weight of the upper lids.

refraction – Test to determine an eye’s refractive error and the best corrective lenses to be prescribed. Series of lenses in graded powers are presented to determine which provide sharpest, clearest vision.

retina – Light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain. Forms a thin membranous lining of the rear two-thirds of the globe.

Snellen chart – Test chart used for assessing visual acuity. Contains rows of letters, numbers, or symbols in standardized graded sizes, with a designated distance at which each row should be legible to a normal eye. Usually tested at 20 ft.

strabismus – Eye misalignment caused by extraocular muscle imbalance: one fovea is not directed at the same object as the other.

sty, stye – Acute pustular infection of the oil glands of Zeis, located in an eyelash follicle at the eyelid margin.

trifocal – Eyeglass lens that incorporates three lenses of different powers. The main portion is usually focused for distance (20 ft.), the center segment for about 2 ft., and the lower segment for near (14 in.).

visual acuity – Assessment of the eye’s ability to distinguish object details and shape, using the smallest identifiable object that can be seen at a specified distance (usually 20 ft. or 16 in.).

vitreous, vitreous humor – Transparent, colorless gelatinous mass that fills the rear two-thirds of the eyeball, between the lens and the retina.

*Excerpted from the Dictionary of Eye Terminology copyright 1990-2007 by Barbara Cassin and Triad Publishing, and from www.eyeglossary.net.