The diseases and conditions which cause blindness, legal blindness, and visual impairment may be grouped into three broad catagories.  Any condition may be congenital (present at birth) or adventitious (developing later in life).  Among congential and adventitious visual impairments are those that stabilize and leave the person with some usable vision and those that deteriorate into blindness.

Broad categories:

• loss of eyes;
• limited visual acuity (blurred vision); or
• limited visual field (areas of missing vision)

The major (and more common) conditions are listed here:

Loss of Eyes:

• Anophthalmia (no eyes)
• Microphthalmia (tiny eyes, too small to function)
• Retinoblastoma (cancer of the eyes, which necessitates removal)
• Trauma

Poor Acuity:

• Albinism (lack of pigment in the retina and iris, with poorly developed retina)
• Amblyopia (eyes focus differently)
• Aniridia (no iris)
• Aphakia (no lens)
• Cataract (hardening, and hence clouding, of the lens)
• Cortical Blindness (unexplained apparent malfunction of the visual centers in the brain)
• Hyperopia (farsightedness)
• Macular Degeneration (deterioration of the macula)
• Myopia (nearsightedness)
• Nystagmus (uncontrolled, constant eye movements)
• Optic Nerve Atrophy (improper formation or function of the optic nerve)
• Presbyopia (eyes cannot change focus for near tasks)
• Retinopathy of Prematurity (retina incompletely developed due to premature birth or retinal damage from excessive oxygen in the incubator)
• Strabismus (eyes misaligned)
• Trauma (with damage to the eye, visual cortex, or optic nerve)

Restricted Field:

• Diabetic Retinopathy (spotting of the visual field due to breakage of blood vessels, or growth of mutant ones)
• Glaucoma (destruction of peripheral retina, resulting in tunnel vision)
• Retinal Detachment (layers of retina splitting apart in one or more spots)
• Retinitis Pigmentosa (destruction of peripheral retina, resulting in tunnel vision)
• Retinopathy of Prematurity (retina incompletely developed due to premature birth, or retinal damage from excessive oxygen in the incubator)
• Trauma (with damage to the retina, visual cortex, or optic nerve)

These lists are very general.  Any individual's condition will be different from a textbook description.  Also, many people are dealing with more than one condition, like the nearsighted person who develops macular degeneration, or the person with glaucoma and cataracts.
 
Click here to see simulations of what people with some visual impairments might see.

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