Improving Cataract Surgical Rates through Better Incidence Estimation

Surgically removable cataracts remain the leading cause of blindness worldwide. The disease is much more common in developing countries due to the absence of ophthalmologists who can perform cataract surgery. Though many factors influence cataract development, the vast majority of cases are age-related and develop in persons over 50 years old. Studies show that women are more susceptible to cataracts and, in Africa, they tend to have less access to treatment. The World Health Organization’s VISION 2020 project, which seeks to eliminate the main causes of avoidable blindness by 2020, includes an important focus on increasing the number of cataract surgeries in Africa [4]. Ideally the number of surgeries performed each year would equal the number of incident cataracts (new cataracts developed) that year. Unfortunately, measuring cataract incidence directly would require surveying the same group of people over a number of years to see when cataracts were developed, a procedure that is often impossible in Africa. For the past several years, because of the lack of data, sub-Saharan Africa has been assumed homogeneous in terms of cataract incidence, and cataract surgical rate (CSR) targets have been equal in these regions. While cataract incidence is difficult to measure, new Rapid Assessment of Avoidable Blindness (RAAB) surveys provide data about age-specific cataract prevalence (the percentage of the population with cataracts in one or both eyes). The challenge is therefore to estimate cataract incidence from prevalence. In simple diseases that are not age-dependent and do not affect death rate, there is a simple dependence between incidence, prevalence, and disease duration, such that any of these can be calculated from the other two. However, cataracts have been shown to affect death rates, and age dependence is an important factor. In a 1986 paper[3], M. Podgor and M. Leske propose one strategy for incidence estimation, which was used in the methods developed by S. Lewallen et. al.[1]. Initial results showed a surprising amount of variation between different parts of sub-Saharan Africa,