Fact Sheet N143
BLINDNESS AND VISUAL DISABILITY
Part II of VII: Major Causes Worldwide
Blindness can occur as a result of a number of infectious and noncommunicable 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:
* A cataract results from a change of transparency of the normal crystalline lens in the eye. When the lens becomes opaque, it impedes the light from entering the eye. This condition causes gradual loss of vision and blindness. Cataract may have different origins: some children can be born with it and some cataracts develop after eye injuries. However, cataracts are largely related to the ageing process.
* The older a person, the more chance there is of developing a cataract. The majority of people with cataracts are over 50 years of age. This means that, as life expectancy increases, more people will develop cataract and the number of blind will increase. By 2020, there will be some 1.2 billion people aged 60 years and over in the world with three-quarters living in developing countries. At present, the causes of ageing-related cataracts are not well known and prevention is therefore not generally possible. However, it seems that protection against excessive UV-irradiation may help prevent at least one form of cataract.
* Usually, ageing-related cataract can be treated with a relatively simple operation to remove the opaque lens. Increasingly, even in developing countries, cataract surgery includes the use of intraocular lens implantation, which, however, requires sophisticated technology and adequately trained personnel. In the USA alone there are some 1.35 million cataract operations performed each year at a cost of US$ 3.4 billion.
* While efforts are being made to increase access to intra ocular lens
implantation through low-cost technology and training of personnel, simple cataract
extraction with provision of spectacles is still practised in the rural areas of many
developing countries, where almost 90% of cataract-related blindness occurs.
* 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.
* The agent is Chlamydia trachomatis - a microorganism resembling both bacteria and viruses, which spreads through contact with eye discharge from the infected person (on towels, handkerchiefs, fingers, etc.) and through transmission by eye-seeking flies. Chlamydia trachomatis provokes an inflammatory reaction in the eye with formation of follicles in the conjunctiva. After years of repeated infections, the inside of the eyelids may be scarred so severely that the eyelid turns inwards with eyelashes rubbing on the eyeball. If untreated, this condition leads to blindness.
* Trachoma and related blindness can be prevented through the implementation of the "SAFE" strategy, which stands for Surgery for trichiasis (inturned eyelashes), Antibiotics, Facial cleanliness and Environmental improvement which is a combination of community-targeted public health interventions.
* Recent field trials of a new and apparently effective drug, azithromycin, have
been very encouraging. This long-acting antibiotic, developed and produced by Pfizer
International, Inc., has been tested in a number of countries. The initial results look
very promising: one dose of azithromycin per year could eliminate the blinding propensity
of trachoma. Once its efficacy has been proven, the challenge will be to find the means to
make this drug available to all those in need.
* A major difficulty with glaucoma, and the irreversible blindness that it can lead to, is the lack of a uniform case definition. The name commonly refers not to a single disease, but to a group of diseases that have certain common features, including, in particular, cupping and atrophy of the optic nerve head, characteristic visual field loss and often, but not invariably, increased intra ocular pressure (IOP).
* Different populations tend to suffer from different types of glaucoma. But, in general, persons of African heritage and Asians are more inclined to develop glaucoma and to lose their sight than Caucasians.
* Early signs of glaucoma are difficult to notice for an individual, except for cases in which pain and blurred vision develop as a result of a sudden increase of intra ocular pressure. Ideally, therefore, persons over 40 years of age should have regular eye examinations, particularly those with a family history of glaucoma.
* Glaucoma as such cannot be prevented, but visual loss can be avoided if the disease is detected and treated at an early stage. Awareness-raising and education aimed at persons at particular risk facilitate the early detection and treatment of glaucoma.
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 country.
For further information, please contact Health Communications and Public Relations, WHO, Geneva (41 22) 791 2532/2599. Fax (41 22) 791 4858.
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