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Abscess - pocket of pus.
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.
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.
Aqueous humor - the clear, watery fluid in the front of the eyeball.
Astigmatism - a vision problem that results in blurred images.
Binocular vision - the ability to use both eyes at once.
Blood vessels - tubes (arteries and veins) that carry blood to and from the eye.
Caruncle - a small, red portion of the corner of the eye that contains modified sebaceous and sweat glands.
Cataract - a change in the structure of the crystalline lens that causes blurred vision.
Choroid - the thin, blood-rich membrane that lies between the retina and the sclera; responsible for supplying blood to the retina.
Ciliary body - the part of the eye that produces aqueous humor (the clear, watery fluid that moves in the eyeball).
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.
Fluorescein stain - a dye placed in the eye. A special light is then used to make the dye "glow" in the eye. Any abrasion or scratch on the cornea can be seen.
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 during development.
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.
Lateral canthus - lateral (side) angle of the eye.
Lens (also called crystalline lens) - the transparent structure inside the eye that focuses light rays onto the retina.
Lower eyelid - lower, inferior, skin that covers the front of the eyeball when closed.
Macula - the focusing portion of the eye that allows us to see fine details clearly.
Medial canthus - medial (middle or center) angle of the eye.
Miosis - constriction of the pupil.
Mydriasis - dilation of the pupil.
Myopia - nearsightedness.
Nonrefractive error - a problem with the eye that results in a decrease in vision. These problems cannot be corrected with eyeglasses alone.
Ophthalmoscopy - examination of the internal structure of the eye.
Optic nerve - a bundle of nerve fibers that connect the retina with the brain. The optic nerve carries signals of light, dark, and colors to the area of the brain (the visual cortex), which assembles the signals into images (i.e., our vision).
Photophobia - sensitivity to light.
Photorefractive keratectomy (PRK) - surgical procedure using an excimer laser to change the shape of the cornea.
Posterior chamber - the back part of the eye's interior.
Posterior optical segment - portion of the eye located behind the crystalline lens, and including vitreous, choroid retina, and optic nerve.
Presbyopia - a form of farsightedness in which it is difficult to focus on close objects or to read and occurs as a child ages.
Pupil - the opening 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 - abnormal shape of the cornea that results in decreased vision. This type of problem can usually be corrected with glasses or contacts.
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.
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.
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.
Upper eyelid - top, movable, superior fold of skin that covers the front of the eyeball when closed, including the cornea.
Visual acuity - the space visible to an eye in a given position of gaze.
Vitreous body - a clear, jelly-like substance that fills the back part of the eye.