Blindness is the partial or complete loss of vision. The leading causes of blindness are glaucoma, cataracts, and diabetic retinopathy. Blindness can also result from eye diseases, optic nerve disorders, or brain diseases involving visual pathways or the occipital lobe of the brain. The patterns of visual field reduction depend on the area that is being affected by disease. Damage to visual pathways as a result of macular degeneration, retinal detachment, or optic nerve atrophy can affect one or both eyes. In contrast, damage to the optic nerve chiasm or the pathway beyond it affects both eyes. There are many eye diseases that can cause visual abnormalities or/and blindness, including retinal detachment, cataracts, retinal disorders (often inherited), and macular degeneration.
Macular degeneration is the leading cause of blindness for those over age 55 in the United States. The macula is the central portion of the retina that records images and sends them from the eye to the brain via the optic nerve. If the macula deteriorates, the eye loses the ability to see in fine detail. The cause of macular degeneration is not fully understood, but risks for the disorder increase with age. Other abnormalities in the central retina can lead to blurry vision or can affect color perception. Color blindness can also originate from the lack of one or more type of cones, a type of light receptor on the eye. Total color blindness (monochromatic vision) is very rare; most commonly, varying levels of single color deficits are found among people with color blindness. Central vision can also be destroyed by small hemorrhages in the retina as a result of the aging process or diabetic retinopathy.
The neuronal diseases affecting the optic nerve and causing blindness can result from developmental abnormalities (hereditary or sporadic), abnormalities in the blood vessels causing an insufficient blood supply to the eyes or optic nerve, glaucoma, and demyelinating and inflammatory diseases such as multiple sclerosis, tumors, toxic agents, and trauma.
Agnieszka Maria Lichanska PhD, The Gale Group Inc., Gale, Detroit,