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.