Term	Definition
accomodation	The eyes' ability to adjust its focus from distant to far objects. This occurs when the lens inside the eye changes shape.
aqueous humor, aqueous fluid	The clear, watery fluid which fill the front of the eye.
astigmatism	See Diseases
blind spot	(1) A small area of the retina where the optic nerve enters the eye (2) Any gap in the visual field that corresponds to an area of the retina where there are no present visual cells.
central vision	The area of vision which is used for fine detail straight ahead. Perfect vision mesure 20/20.
ciliary muscles	The muscles in the eye which enable the lens to change its shape for focusing.
cones	A cone is one of the two types of light receptor cell in the retina. Cones best see fine detail and color.
conjuctiva	A mucous membrane that lines the inner surfaces of the eyelids and the outside of the white of the eye.
cornea	The cornea is a clear, strong layer on the surface ofe the eye; that covers the iris and the pupil.
dialation	The enlargement of the pupil. This is usually done with eyedrops.
fundus	The eye's interior, which is best seen after dialation.
hyperopia	Farsightedness
intraocular pressure (IOP)	Fluid pressure inside the eye
iris	The colored area of the eye surrounding the pupil.
lens	A natural internal foucusing structure of the eye.
legal blindness	In the U.S., when a person's visual acuity is of 20/200 or worse in the better eye with corrective lenses.
macula	The central section of the retina where most of the cones are located. Used for fine detail vision
myopia	Nearsightedness
optic disc	Where the optic nerve connects to the retina.
optic nerve	The nerve that sends messages form the brain to the eye.
peripheral vision	Side vision
pupil	Black circle in the center of the iris that opens and closes to allow light in the eye.
retina	The layer of light receptor cells at the back of the eye that forms an image that is sent ot the brain.
rods, rod cells	One of the two types of light receptor cells in the retina. Rods see dim light and provide peripheral vision.
sclera	The white, tough, outer layer of the eyeball. It and the cornea protect the entire eyeball.
trabecular meshwork	The place where fluid drains out of the eye.
visual acuity	The ability to see fine detail. Vision that is perfect is measured as 20/20.
visual field	The entire are in which the eye can see from side to side (this includes peripheral vision).
vitreous	Thick, gelatinous material which fills the back of the eye in front of the retina.