Words Worth Knowing- The Structure of the Human Eye

sclera

white, opaque, and tough covering of the eye that protects it; nourished by capillaries that supply oxygen to it (red squiggly lines that are visible on the whites of your eyes)

cornea

clear and transparent; positioned in front of the pupil and iris and protects them; nourished by aqueous humor and tears produced by lacrimal glands

lacrimal glands

located above each eye in the upper lid; secretes fluid (tears) to lubricate and moisten the surface of the eye

iris

circular muscles surrounding the pupil; helps regulate amount of light entering the eye; different colors due to lack or concentration of melanin (pigment)

pupil

opening in the middle of the eye; regulates amount of light entering the eye with the help of the iris; sensitive to light

ciliary muscles

these muscles around the lens hold it in place and change its shape to adjust to focus on objects at different distances

acqueous humor

clear, watery fluid behind the cornea; nourishes the cornea and works with it to help focus light

lens

colorless; nearly transparent; focuses light rays onto retina; behind iris and pupil; ciliary muscles contract, lens thickens, focus on near objects; muscles relax, lens flattens, focus on far objects

vitreous humor

clear, jelly-like fluid; holds internal structure in place; gives shape to the eye ball; fills up posterior chamber

retina

thin, innermost layer; sensitive to light; absorbs light entering the eye

choroid

second layer between sclera and retina; contains blood vessels to nourish retina

macula

concentration of cone cells; processes clear sharp vision; located in the center of the retina

fovea

dip in macula; only cone cells; highest sensitivity

optic disk

all, white, oval-shaped area on the retina; beginning of the optic nerve

blind spot

the optic disk; called the "blind spot" because the area is absent of photoreceptors to images cannot be processed in this area

optic nerve

begins at optic disk, located at the back of the eye; carries sensory information from retina's photoreceptors to visual centers of the brain