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These links take you off-site. Here are the codes to where:


AAV = All About Vision

AFB = American Foundation for the Blind

AOA = American Optometric Association

APH = American Printing House for the Blind

CRF = Cornea Research Foundation

FB = Fighting Blindness (Irish)

FFB = Foundation Fighting Blindness

MAYO = Mayo Clinic

MED = Medline Plus (NIH)

NIH = National Institutes of Health

NORD = National Organization for Rare Disorders

RNIB = Royal National Institute of Blind People (British)

SG = Support Group or focused Specialty Group

UofA = The University of Arizona

Achromatopsia NIH FB SG

Albinism NIH VisionAware SG

Amblyopia NIH SG

Aniridia NIH SG

Anophthalmia and Microphthalmia NIH

Aphakia, Congenital NIH UofA

Astigmatism NIH AOA MAYO

Bardet-Biedl Syndrome NIH NORD SG

Best Disease RNIB FB

Blue-Cone Monochromacy FFB Orphanet

Cataracts NIH MAYO

CHARGE Syndrome: see also Coloboma. NIH

Charles Bonnet syndrome RNIB AFB SG

Choroideremia FB SG

Coloboma: see also CHARGE Syndrome NIH

Color Blindness NIH

Corneal Disease NIH CRF

Corneal Dystrophy, Fuchs' MAYO SG SG SG

Cortical Visual Impairment Neurological AFB APH

Dry Eye Syndrome NIH MAYO

Dysplasia: see Hypoplasia

Dystrophy (Cone-Rod) NIH FB

Exudative Vitreoretinopathy (Familial) NIH OrphaNet ASRS SG

Farsightedness: see Hyperopia

Floaters and Spots NIH MAYO

Glaucoma NIH SG

Hemianopia NIH SG

Hyperopia (Farsightedness) NIH

Hypopigmentation (see also Albinism) SG

Hypoplasia (Optic Nerve) NIH SG SG

Keratoconus CRF SG

Keratopathy (Bullous) CRF

Laurence-Moon-Bardet-Biedl Syndrome NIH SG

Leber Congenital Amaurosis FB

Leber’s Hereditary Optic Neuropathy (LHON) NIH FB SG

Low Vision NIH SG

Macular Degeneration (age related) NIH FB SG

Macular Edema, Diabetic NIH MAYO

Macular Pucker NIH

Macular Hole NIH

Malattia Leventinese NIH FFB

Marfan Syndrome NIH SG

Microphthalmia: see Anophthalmia

Myopia (Nearsightedness) NIH AOA

Nystagmus AOA AAV SG

Oguchi Disease NIH FFB

Photophobia MED

Presbyopia NIH

Refsum NIH SG

Retinal Detachment NIH FB SG

Retinitis Pigmentosa NIH FB

Retinoblastoma NIH SG

Retinopathy of Prematurity NIH

Retinopathy (Diabetic) AFB NIH MAYO

Retinoschisis, Juvenile X-linked FB

Retrolental Fibroplasia: see Retinopathy of Prematurity.

Rod-Cone Dystrophy: see Dystrophy

Scotoma WIKI

Stargardt Disease (Stargardt Juvenile Macular Dystrophy) NIH FB

Strabismus (see also Amblyopia) NIH Medline SG

Sturge-Weber Syndrome NIH SG

Trachoma NIH MAYO SG

Usher Syndrome NIH FB SG

Uveitis NIH SG

Vitelliform Macular Dystrophy: see Best Disease.



The cornea is a transparent dome-shaped tissue that forms the front part of your eye. It functions as a window and allows light to enter your eye. It also begins the process of focusing light rays that allow you to see words and images clearly. The cornea does not contain any blood vessels, but instead contains nerve endings that make it extremely sensitive. That is why a scratch or a loose eyelash is so painful.

Aqueous humor is a clear, watery fluid contained in a chamber behind the cornea that helps bring nutrients to the ocular tissue. It is made behind the lens and flows to the front of the eye, where it is drained by a tissue called the trabecular meshwork. Problems with the flow of this fluid can lead to problems with the pressure inside the eye.

The sclera is a tough white outer coating of fibrous tissue that covers your entire eyeball (all the way around) except for the cornea. The muscles that move the eye are attached to the sclera. The name sclera comes from the Greek word "skleros," which means "hard."

The iris is a tissue inside the eye that has a hole in the center called the pupil. The iris contains muscles that allow the pupil to become larger (open up or dilate) and smaller (close up or constrict). The iris regulates the amount of light that enters your eye by adjusting the size of the pupil opening. In bright light, the iris closes (or constricts) and makes the pupil opening smaller to restrict the amount of light that enters your eye.In dim light, the iris opens (or dilates) and makes the pupil opening larger to increase the amount of light that enters your eye. In addition, it is the iris that determines your eye color. People with brown eyes have heavily pigmented irises, while people with blue or lighter-colored eyes have irises with less pigment. Therefore, people with lighter-colored eyes should wear sunglasses outdoors, especially during the summer. According to Prevent Blindness America, extended exposure to ultraviolet (UV) light (such as sunlight) has been linked with cataracts and macular degeneration.

The choroid is a dark brown membrane that is rich with blood vessels, located between the sclera and the retina. It supplies blood and nutrients to the retina and nourishes all of the other structures within the eye.

The vitreous is the jelly-like substance that fills the inside of the back part of the eye. Over time, the vitreous becomes more liquid and can detach from the back part of the eye, which can create "floaters." If you notice new floaters or flashing lights, it is important to see an eye doctor, because a detached vitreous can cause a hole (a condition called a "macular hole") to develop in the retina.

The retina is the light-sensitive tissue that lines the inside surface of the eye, much like wallpaper. Cells in the retina convert incoming light into electrical impulses. These electrical impulses are carried by the optic nerve (which resembles your television cable) to the brain, which finally interprets them as visual images.

The macula is the small sensitive area in the center of the retina that provides clear central vision. The fovea is located in the center of the macula and provides the sharpest detail vision.

The lens is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina. Because the lens is flexible and elastic, it can change its curved shape to focus on objects and people that are either nearby or at a distance. A more rounded lens can focus on near objects, a more elongated (or stretched) lens can focus on objects that are far away.
The ciliary muscles, which are part of the ciliary body, are attached to the lens and contract or release to change the lens shape and curvature. The lens becomes more rounded to focus on near objects. Over time, the lens loses some of its elasticity and therefore loses some of its ability to focus on near objects. This is called "presbyopia" and explains why people need reading glasses as they become older.

The National Library of Medicine is a division of the National Institutes of Health. They have a database of more than 750 of the most common genetic diseases on a page they call Genetics Home Reference. It provides consumer-friendly information about the effects of genetic variations on human health. Use their search box function at the top of their page.


Legal Blindness is a level of visual impairment that has been defined by law to determine eligibility for benefits. It refers to central visual acuity of 20/200 or less in the better eye with the best possible correction, or a visual field of 20 degrees or less.