Nine out of ten of persons who are blind live in the developing world. The major causes of avoidable blindness and serious visual impairment worldwide include cataract, trachoma and glaucoma. Cataract accounts for approximately 16 million cases of blindness worldwide. In most countries of Africa and Asia, it accounts for approximately half of all blindness. The majority of persons with cataracts are over 50 years of age.
Trachoma is one of the oldest infectious diseases know to mankind.
Worldwide, there are about 6 million persons blinded by trachoma and an estimated 146 million cases of active disease in need of treatment, if blindness is to be prevented. Glaucoma is considered to be the third largest cause of blindness worldwide, and is responsible for an estimated 5.2 million cases. Estimates prepared by WHO put the total number of suspected cases of glaucoma at around 105 million. Their individual relative importance varies greatly by region and sometimes by country. Apart from cataract, trachoma and glaucoma, there are other leading causes of preventable blindness and visual impairment.