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Abnormalities and injuries

Eye injuries, most often occurring in people under 30, are the leading cause of monocular blindness (vision loss in one eye) throughout the United States. Injuries and cataracts affect the eye itself, while abnormalities such as optic nerve hypoplasia affect the nerve bundle that sends signals from the eye to the back of the brain, which can lead to decreased visual acuity.

People with injuries to the occipital lobe of the brain can, despite having undamaged eyes and optic nerves, still be legally or totally blind.
[edit] Genetic defects

People with albinism often have vision loss to the extent that many are legally blind, though few of them actually cannot see. Leber's congenital amaurosis can cause total blindness or severe sight loss from birth or early childhood.

Recent advances in mapping of the human genome have identified other genetic causes of low vision or blindness. One such example is Bardet-Biedl syndrome.
[edit] Poisoning

Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol, which is only mildly toxic and minimally intoxicating, but when not competing with ethanol for metabolism, methanol breaks down into the substances formaldehyde and formic acid which in turn can cause blindness, an array of other health complications, and death.[15] Methanol is commonly found in methylated spirits, denatured ethyl alcohol, to avoid paying taxes on selling ethanol intended for human consumption. Methylated spirits are sometimes used by alcoholics as a desperate and cheap substitute for regular ethanol alcoholic beverages.
[edit] Willful actions

Blinding has been used as an act of vengeance and torture in some instances, to deprive a person of a major sense by which they can navigate or interact within the world, act fully independently, and be aware of events surrounding them. An example from the classical realm is Oedipus, who gouges out his own eyes after realizing that he fulfilled the awful prophecy spoken of him. Having crushed the Bulgarians, the Byzantine Emperor Basil II blinded as many as 15,000 prisoners taken in the battle, before releasing them.[16]

In 2003, a Pakistani anti-terrorism court sentenced a man to be blinded after he carried out an acid attack against his fiancee that resulted in her blinding.[17] The same sentence was given in 2009 for the man who blinded Ameneh Bahrami.
[edit] Comorbidities

Blindness can occur in combination with such conditions as mental retardation, autism spectrum disorders, cerebral palsy, hearing impairments, and epilepsy.[18][19] In a study of 228 visually impaired children in metropolitan Atlanta between 1991 and 1993, 154 (68%) had an additional disability besides visual impairment.[18] Blindness in combination with hearing loss is known as deafblindness.

12 years ago. Rating: 2
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Serious visual impairment has a variety of causes:
[edit] Diseases

According to WHO estimates, the most common causes of blindness around the world in 2002 were:

1. cataracts (47.9%),
2. glaucoma (12.3%),
3. age-related macular degeneration (8.7%),
4. corneal opacity (5.1%), and
5. diabetic retinopathy (4.8%),
6. childhood blindness (3.9%),
7. trachoma (3.6%)
8. onchocerciasis (0.8%).[13]

In terms of the worldwide prevalence of blindness, the vastly greater number of people in the developing world and the greater likelihood of their being affected mean that the causes of blindness in those areas are numerically more important. Cataract is responsible for more than 22 million cases of blindness and glaucoma 6 million, while leprosy and onchocerciasis each blind approximately 1 million individuals worldwide. The number of individuals blind from trachoma has dropped dramatically in the past 10 years from 6 million to 1.3 million, putting it in seventh place on the list of causes of blindness worldwide. Xerophthalmia is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind. Central corneal ulceration is also a significant cause of monocular blindness worldwide, accounting for an estimated 850,000 cases of corneal blindness every year in the Indian subcontinent alone. As a result, corneal scarring from all causes now is the fourth greatest cause of global blindness (Vaughan & Asbury's General Ophthalmology, 17e)

People in developing countries are significantly more likely to experience visual impairment as a consequence of treatable or preventable conditions than are their counterparts in the developed world. While vision impairment is most common in people over age 60 across all regions, children in poorer communities are more likely to be affected by blinding diseases than are their more affluent peers.

The link between poverty and treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in North America and Western Europe is related to age-related macular degeneration and diabetic retinopathy. While both of these conditions are subject to treatment, neither can be cured.

In developing countries, wherein people have shorter life expectancies, cataracts and water-borne parasites—both of which can be treated effectively—are most often the culprits (see river blindness, for example). Of the estimated 40 million blind people located around the world, 70–80% can have some or all of their sight restored through treatment.[citation needed]

In developed countries where parasitic diseases are less common and cataract surgery is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness.[14]

Childhood blindness can be caused by conditions related to pregnancy, such as congenital rubella syndrome and retinopathy of prematurity.

12 years ago. Rating: 2
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