|Legal blindness is visual acuity of not greater than 20/200
in the better eye with best correction or a visual field of less
than 20 degrees. Legal blindness can mean tunnel vision, no central
vision, cloudy or extremely blurred vision, seeing just shadows,
or no vision at all.
does 20/200 mean?
A person with normal visual acuity can see
an object clearly, at 200 feet; a legally blind person must
be 20 feet or closer to see the same object.
Blindness can occur as a result of a number
of infectious and no communicable diseases, as well as injuries.
Depending on the cause, up to 80% of blindness and serious
visual loss could be avoided (prevented or treated). The
main causes of avoidable blindness and serious visual impairment
worldwide include cataract, trachoma and glaucoma.
|Opacities and clouding of the eye's lens, known as cataracts,
which may form and block the passage of light through the eye.
Some people are born with cataracts, but the incidence increases
with age. They are not painful, in fact the only symptom is blurred,
dimmed or double vision. Not all require surgery, but those large
enough to cause serious visual problems require surgical removal
of the lens, implantation of an intraocular lens and corrective
glasses or contact lenses.
|Perhaps one in every seven or eight cases of blindness
is due to this disorder, in which the transparent fluid inside
the forward part of the eye does not drain normally and excess
pressure is built up within the eye. If the pressure is not controlled,
the delicate structure of the eye is increasingly damaged, resulting
in blurred vision, a narrowed field of sight and eventually total
blindness. Early symptoms may include blurred vision, halos around
lights and reduced side vision. In the acute type, there is great
pain as eye pressure rises quickly from blocked drainage canals.
In the more common chronic type there is no pain and vision loss
is gradual. Many cases are controlled very well by medication,
but surgery is sometimes necessary. Early detection is important.
This is one of the oldest infectious diseases known to
mankind. It is responsible, at present, for 15 % of the world's
blindness. Worldwide, there are about 6 million people largely
irreversibly blinded by trachoma and an estimated 146 million
cases of active disease in need of treatment, if blindness is
to be prevented. Today, the disease is found mainly in poor
rural areas of most African countries, some countries in the
Eastern Mediterranean, and in certain parts of Central and South
America. Trachoma is still endemic in several Asian countries,
but there is a lack of updated information from some major populations,
such as India and China.
Cataract, trachoma and glaucoma together account for
more than 70 % of the world's blindness. In India the three
diseases account for about 74% of those who are blind, in China
- about 73%, in other countries of Asia and island countries
- about 80%, and in Sub-Saharan Africa - 75%. Their individual
relative importance varies greatly by region and sometimes by