Glossary of Terms

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Albinism	People with albinism have absent or reduced pigment in their eyes, skin or hair. They have inherited genes that do not make the usual amounts of a pigment called melanin which is essential for the full development of the retina. Lack of melanin in development of the retina is the primary cause of visual impairment in albinism.
Aniridia	A hereditary eye problem in which the iris, the colored part of the eye, is absent. There is poor vision, sensitivity to sunlight, nystagmus, and a tendency to develop glaucoma.
Aphakia	Absence of the lens, usually because of cataract extraction.
Aqueous	A clear watery fluid that fills the space between the cornea and the vitreous. It is responsible for nourishing the cornea, iris, lens and maintaining the intraocular pressure.
Astigmatism	Light entering the eye focuses at two different points neither of which may be on the retina resulting in a blurred image. This is referred to as astigmatism. It is the result of the optical components of the eye - the cornea and the lens - having a non-spherical shape. Eyeglasses are required in many situations to accurately achieve focus on the retina.
Canal of Schlemm	Responsible for moving the aqueous from the front chamber in the eye through aqueous veins into the bloodstream.
Cataracts	A condition of the crystalline lens, in which the normally clear lens becomes clouded or yellowed, causing blurred or foggy vision. Cataracts may be caused by aging, eye injuries, disease, heredity, or birth defects.
Chorioretinitis	An inflammation of the back of the eye involving the choroid and retina. It may be due to a number of different diseases, which affect the body such as toxoplasmosis, histoplasmosis, sarcoidosis, tuberculosis and syphilis.
Choroid	A layer of the eye found between the retina and the sclera. It contains major blood vessels and provides nourishment to the outer layers of the retina.
Ciliary Body	Made up of ciliary muscle which helps the accomodation of the lens and controls the intraocular pressure of the eye. It is also where the aqueous is made.
Coloboma	A congenital problem with the eye that is related to a maldevelopment or underdevelopment of a part of the eye. It may involve the eyelid, or interior part of the eye (involving the choroid and occasionally the optic nerve).
Cones	Light sensitive receptor cells mostly found in the central part of the retina. It is responsible for sharp visual acuity and the discrimination of color.
Conjunctiva	A transparent mucous membrane the covers the outer surface of the eyeball except the cornea. It also lines the inner surface of the eyelid.
Cornea	The clear cone over the front part of the eye. It is is responsible for most of the eyes optical power.
Cortical Visual Impairment(CVI)	A temporary or permanent visual impairment caused by the disturbance of the posterior visual pathways and/or the occipital lobes of the brain. The degree of vision impairment can range from severe visual impairment to total blindness. The degree of neurological damage and visual impairment depends upon the time of onset, as well as the location and intensity of the insult. It is a condition that indicates that the visual systems of the brain do not consistently understand or interpret what the eyes see.
Emmetropia	Light entering the eye focuses exactly on the retina creating a sharp image. In this situation, no glasses are required for correction.
Field of Vision	The entire area that can be seen without shifting the head or the eyes, including central and peripheral fields.
Fovea	Located in the center of the macula. It provides the sharpest vision.
Glaucoma	A symptomatic condition characterized by raised intra-ocular pressure, visual field loss, enlargement of the blind spot and changes in the appearance of the optic nerve head. If left untreated ganglion cell axon death may be caused by prolonged exposure of the eye to elevated introcular pressure.
Hemianopia	A loss of one-half of the field of vision; for example, all of the right side of vision is gone. This is sometimes seen in older people with vascular problems, in certain types of brain tumors or after head trauma.
Hyperopia	Light entering the eye focuses behind the retina creating a blurred image. This is referred to as farsightedness. Depending on the degree of hyperopia both distance and near vision may be effected. Children and young adults have the ability to compensate for modest degrees of hyperopia without eyeglass correction. Eyeglasses are required in many situations to accurately achieve focus on the retina.
Iris	A colored circular muscle that gives us the color of our eyes. It is responsible for controlling the amount of light that gets into the eye.
Leber's Amaurosis	A severe form of rod-cone degeneration present at birth. Infant's have very poor visual acuity, photophobia and nystagmus. Infant's with Leber's will often constantly rub their eyes with their fists and poke their eyes with their fingers and thumb.
Lens	Responsible for bringing rays of light into focus on the retina. It is a clear oval structure suspended behind the iris which can contract and expand as needed to provide additional focusing power.
Macula	A small central area of the retina responsible for fine central visual acuity.
Myopia	Light entering the eye focuses in front of the retina creating a blurred image. This is referred to commonly as nearsightedness. Generally objects at a close range are clear, but at a distance blur is created. Glasses are required to focus light on the retina for a clear image.
Optic Giloma	Inflammation of the optic nerve; can produce a sudden, but reversible, loss of sight.
Optic Nerve	Carries the light impulses for sight from the retina to the brain.
Optic Nerve Atrophy	is a permanent visual impairment caused by damage to the optic nerve
Optic Nerve Hypoplasia	Refers to underdevelopment of the optic nerve during pregnancy
Refraction	Refraction is the term used to describe the various testing procedures employed in the measurement of the optical characteristics of the eye.
Refractive Errors	This term denotes the specific optical character of the eye. The eye is like a camera. The focusing elements of the eye are the cornea and the lens. The film is the retina. When light enters the eye it is bent by the cornea and the lens and focused on the retina (film) to create a clear image. If light is not exactly focused on the retina due to a mismatch in the power of the cornea and lens, a blurred image results. Eyeglasses are an optical device used to correct this defocused image. The following terms describe the various refractive states of the eye: Emmetropia, Myopia, Hyperopia, Astigmatism.
Retina	The innermost layer of the eye, a neurological tissue, which receives light rays focused on it by the lens. This tissue contains receptor cells (rods and cones) that send electrical impulses to the brain via the optic nerve when the light rays are present.
Retinal Detachment	The separation of the sensory layer from the pigment layer of the retina.
Retinitis Pigementosa	A disease of the photoreceptors, frequently inherited, which at its most advanced stage allows only a tiny island of central vision.
Retinoblastoma	The most common cancer in the eye occurring in early childhood. A parent or doctor may first suspect a problem by detecting whiteness in the normally dark pupil. Occasionally it leads to a wandering eye (strabismus). It does not spread from one eye to the other but about 25% have a tumor in each eye. Immediate medical treatment is necessary. Sometimes the eye(s) must be removed to prevent spreading of the tumor into the brain.
Retinopathy of Premturity (ROP)	An eye disorder affecting premature infants. This disorder was called Retrolental Fibroplasia in the past. ROP affects immature blood vessels of the retina. It occurs weeks after birth. Once development of blood vessels is complete, a child is no longer a candidate for this disorder.
Rods	Light sensitive receptor cells mostly found in the peripheral part of the retina. They are responsible for night vision.
Sclera	The protective outer layer of the eye.
Visual Acuity	The ability to discern fine detail.
Vitreous	A clear jello-like substance between the lens and the retina that provides the structural support to the eye.