National survey; Sample size: 8702; Reference: Kyari F, Gudlavalleti MV, Sivsubramaniam S, Gilbert CE, Abdull MM, Entekume G, Foster A; Prevalence of blindness and visual impairment in Nigeria: the National Blindness and Visual impairment Study. Invest Ophthalmol Vis Sci. 2009 May;50 (5):2033-9 and Contact Dr Jacqui Ramke for details of calculations to make national survey results compatible with RAAB generated data   jramke@gmail.com