Estimating Incidence of Vision-Reducing Cataract in Africa

Abstract

To estimate the incidence of vision-reducing cataract in sub-Saharan Africa and use these data to calculate cataract surgical rates (CSR) needed to eliminate blindness and visual impairment due to cataract. Methods: Using data from recent population-based, standardized, rapid-assessment surveys, we calculated the agespecific prevalence of cataract (including operated and unoperated eyes) from surveys in 7 "districts" across Africa. This was done at 3 levels of visual acuity. Then we used the age-specific prevalence data to develop a model to estimate age-specific incidence at different visual acuities, taking into account differences in mortality rates between those with cataract compared with those without. The model included development of opacity in the first eye and second eye of people older than 50 years. The incidence data were used to calculate target cataract surgical rates. Results: Incidence and CSR needs varied significantly in different sites and were lower in some than expected. Cataract surgical rates may depend on genetic, environmental, or cultural variations and will vary with population structure, which is not uniform across Africa. Conclusion: Africa should not be viewed as homogeneous in terms of cataract incidence or CSR needed. These CSR calculations should be useful for more appropriate planning of human resources and service delivery on the continent. The methodology can be applied to other population-based data as they become available to determine appropriate CSR targets.

Elimination of avoidable blindness due to cataract: Where do we prioritize and how should we monitor this decade?

“…What these examples also highlight is that district/regional planning of cataract surgical services is crucial for success. This is a critical determinant for planning cataract programs as is documented by the recent papers from Africa,[50] wherein the importance of the local situation is strongly emphasized also exhibiting that there cannot be a policy of ‘one-shoe-fits-all’ with regard to required CSR or cataract dynamics in different populations.…”

Task shifting for cataract surgery in eastern Africa: productivity and attrition of non-physician cataract surgeons in Kenya, Malawi and Tanzania

“…Based on recent estimates of cataract prevalence, District level hospitals may not serve a large enough population to have adequate cases, if surgery is limited to eyes with a vision <3/60 or <6/60 [2,3]. If Ministries of Health place NPCSs in these settings, productivity will likely remain low and national targets for cataract surgery will not be achieved.…”

“…For individual countries, the known prevalence of vision loss due to cataract can be used to estimate the number of cataract operations (incident cases) needed to eliminate blindness or visual impairment due to cataract [2,3]. Achieving this level of productivity and improved quality of outcomes [4] would eliminate blindness due to cataract [5] and result in achievement of the International Agency for the Prevention of Blindness, VISION 2020 goals.…”

Blindness and cataract surgical services in Atsinanana region, Madagascar

“…Therefore, a decision was made for the RAAB to sample only villages within a two-hour walk from the nearest road, recognizing that the results would represent the prevalence and causes of visual impairment in populations with relatively better access to services. For modeling the incidence of operable cataract and the cataract surgical rate (CSR) required to deal with these, the sample from this special population with access should be representative of the whole population since the model does not depend on service delivery 9. The CSR is defined as the number of surgeries per million population per year.…”