Medical Terminology Chapter 17

anterior chamber

Area behind the cornea and in front of the lens and iris. It contains aqueous humor.

refraction

Bending of light rays by the cornea, lens, and fluids of the eye to bring the rays into focus on the retina. Refract means to break (-fract) back (re-).

pupil

Central opening of the eye, surrounded by the iris, through which light rays pass. It appears dark.

biconvex

Consisting of two surfaces that are rounded, elevated, and curved evenly, like part of a sphere. The lens of the eye is a biconvex body.

conjuctiva

Delicate membrane lining the undersurface of the eyelids and covering the anterior eyeball.

cornea

Fibrous transparent layer of clear tissue that extends over the anterior portion of the eyeball. Derived from Latin "corneus" meaning horny, perhaps because as it protrudes outward, it was thought to resemble a horn.

aqueous humor

Fluid produced by the ciliary body and found in the anterior chamber. A humor (Latin humidus means moist) is any body fluid, including blood and lymph.

retina

Light-sensitive nerve cell layer of the eye containing photoreceptor cells (rods and cones).

choroid

Middle, vascular layer of the eye, between the retina and the sclera.

accommodation

Normal adjustment of the eye to focus on objects from far to near. The ciliary body adjusts to the lens (rounding it) and the pupil constricts. When the eye focuses from near to far, the ciliary body flattens the lens and the pupil dilates.

cone

Photoreceptor cell in the retina that transforms light energy into a nerve impulse. Cones are responsible for color and central vision.

rod

Photoreceptor cell of the retina essential for vision in dim light and for peripheral vision.

iris

Pigmented (colored) layer that opens and closes to allow more or less light into the eye. The central opening of the iris is the pupil.

optic chiasm

Point at which optic nerve fibers cross in the brain (Latin "chiasma" means crossing).

fundus of the eye

Posterior, inner part of the eye.

optic disc

Region at the back of the eye where optic nerve meets the retina. It is the blind spot of the eye because it contains only nerve fibers, no rods or cones, and is thus insensitive to light.

thalamus

Relay center of the brain. Optic nerve fibers pass through the thalamus on their way to the cerebral cortex.

vitreous humor

Soft, jelly-like material behind the lens in the vitreous chamber; helps maintain the shape of the eyeball.

ciliary body

Structure surrounding the lens that connects the choroid and iris. It contains ciliary muscles, which control the shape of the lens, and it secretes aqueous humor.

fovea centralis

Tiny pit or depression in the retina that is the region of clearest vision.

sclera

Tough, white outer coat of the eyeball.

lens

Transparent, biconvex body behind the pupil of the eye. It bends (refracts) light rays to bring them into focus on the retina.

macula

Yellowish region on the retina lateral to and slightly below the optic disc; contains the fovea centralis, which is the area of clearest vision.