Cataract: the leading cause of blindness and vision loss in Africa.

Senile cataract is a non-preventable disease of aging, having its biggest impact in the over-60 age group. Published clinic and hospital data, population-based surveys and World Health Organization estimates indicate that 1.2% of the entire population of Africa is blind, and that cataract causes 36% of this blindness. Ocular disease and ophthalmic manpower status questionnaires mailed to every African country in 1982 by the International Eye Foundation support these contentions, and further demonstrate that cataract is the biggest single cause of blindness on the continent. Taking the population of Africa as a whole, this means that 6,000,000 people are blind, and that 2,000,000 of them are blind due to cataract. As this form of blindness is so closely related to aging, an estimate of the annual incidence of the condition can be made. One method is to use the formula I = P/D, where I = annual incidence, P = overall prevalence and D = duration of the condition. A 5-year survival has come to be a commonly used estimate in developing world epidemiology for the longevity of a person who becomes blind due to senile onset cataracts. In Africa then, I = P/D = 2,000,000/5 = 400,000 people blinded annually by cataract. An alternate method for this computation is to multiply the number of people entering the 60 and above age group annually by 0.08. This factor is derived from knowing the prevalence of cataract blindness in this age group, the life expectancy on becoming 60, and the number of people turning 60 annually. This gives an annual incidence of 160,000 and would signify that the development of cataract blindness does not reduce longevity. Follow-up prevalence surveys in the same population group will tell us which method (if either) is correct. The average number of cataract operations done annually by each ophthalmologist in Africa is surprisingly low, 120. The two most cost-effective ways of raising the number of cases done are: (1) shorten the average hospital stay, and (2) train more ophthalmic clinical officers to perform cataract surgery.