accommodation - the ability of the eye to focus.
amblyopia - sometimes called "lazy eye;" is the reduction or dimming of vision in an eye that appears to be normal.
Amsler grid - a chart featuring horizontal and vertical lines used to test vision.
anterior chamber - the front section of the eye's interior where aqueous humor flows in and out of providing nourishment to the eye and surrounding tissues.
astigmatism - a vision problem that results in blurred images.
binocular vision - the ability to use both eyes at once.
cataract - a change in the structure of the crystalline lens that causes blurred vision.
choroid - the thin, blood-rich membrane that covers the white of the eyeball; responsible for supplying blood to the retina.
ciliary body - the part of the eye that produces aqueous humor.
conjunctiva - the membrane that lines the exposed eyeball and the inside of the eyelid.
conjunctivitis - inflammation of the conjunctiva of the eye.
cornea - the clear, dome-shaped surface that covers the front of the eye.
corneal curvature - the shape of the front surface of the eye.
depth perception - the ability to distinguish objects in a visual field.
diplopia - double vision.
glaucoma - increased intraocular pressure that can result in optic nerve damage and loss of sight.
hyaloid canal - narrow passageway that allows blood to flow through the eye.
hyperopia - farsightedness.
iris - the colored part of the eye. The iris is partly responsible for regulating the amount of light permitted to enter the eye.
keratitis - inflammation of the cornea.
lens (also called crystalline lens) - the transparent structure inside the eye that focuses light rays onto the retina.
macula - the portion of the eye that allows us to see fine details clearly.
macular degeneration - degeneration in the macular region of the retina that results in decreased central vision and sometimes, in blindness.
miosis - constriction of the pupil.
mydriasis - dilation of the pupil.
myopia - nearsightedness.
near point of accommodation - the closest point in front of the eyes that an object may be clearly focused.
near point of convergence - the maximum extent the two eyes can be turned inward.
ocular hypertension - high (greater than 21 mm Hg) intraocular pressure.
ophthalmoscopy - examination of the internal structure of the eye.
orthokeratology - the use of contact lenses to change the shape of the cornea in order to correct refractive error.
optic nerve - a bundle of more than one million nerve fibers that connects the retina with the brain. The optic nerve is responsible for interpreting the impulses it receives into images.
photophobia - sensitivity to light.
photorefractive keratectomy (PRK) - surgical procedure using an excimer laser to change the shape of the cornea.
pinguecula - irritation caused by the degeneration of the conjunctiva.
posterior chamber - the back section of the eye's interior.
posterior optical segment - portion of the eye located behind the crystalline lens, and including the vitreous, choroid, retina, and optic nerve.
posterior vitreous detachment (PVD) - the separation of the vitreous from the retina.
presbyopia - a form of farsightedness in which it is difficult to focus on close objects or to read.
pupil - the dark center in the middle of the iris through which light passes to the back of the eye.
pupillary response - the constriction or dilation of the pupil as stimulated by light.
radial keratotomy - a surgical procedure in which incisions are made into the epithelium of the cornea to correct refractive error.
refractive error - the degree to which light reaches the back of the eye - myopia, hyperopia, astigmatism.
retina - the light-sensitive nerve layer that lines the back of the eye. The retina senses light and creates impulses that are sent through the optic nerve to the brain.
retinal detachment - separation of the retina from the epithelium layer and from its blood supply.
sclera - the white visible portion of the eyeball. The muscles that move the eyeball are attached to the sclera.
scotoma - an area of partial or complete loss of vision surrounded by an area of normal vision.
stereopsis - ability to perceive three-dimensional depth.
suspensory ligament of lens - a series of fibers that connect the ciliary body of the eye with the lens, holding it in place.
tonometry - test to measure intraocular pressure for glaucoma.
visual acuity - the space visible to an eye in a given position of gaze.
vitreous body - a clear, jelly-like substance that fills the center of the eye.