Low Prevalence of Bilateral (Presumed Nutritional) Optic Neuropathy as a Cause of Blindness in The Gambia

Abstract

Previous reports of epidemics of optic neuropathy in Africa have mainly focused on eastern and central areas. Our study aimed to measure the prevalence of optic neuropathy in The Gambia, a West African country, and compare this prevalence with a simultaneously occurring epidemic of optic neuropathy, now considered endemic, in Tanzania. The sample population, derived from the Gambian National Blindness Survey (1996), was selected using simple random sampling. Thirty-three cases of low vision/blindness were identified where optic neuropathy was the sole cause of visual loss. Within a month, 31 cases were located and these patients underwent ophthalmic and peripheral nerve assessment and completed lifestyle questionnaires. Five of the 31 individuals were found to have bilateral symmetrical optic neuropathy. Although it was not possible to fully ascertain etiology, the phenotype is compatible with epidemic, presumed nutritional, optic neuropathy described in Tanzania. Comparative prevalence data suggest a prevalence of 0.07% in The Gambia based on a total sample size of 6873 vs 2.4% in Tanzania. Our data indicate that bilateral optic neuropathy is nonepidemic in The Gambia. Rare vitamin B12 and folate deficiencies reported in rural Gambians may explain the low prevalence because previous epidemics were due to nutrient deficiency. Our study is the only available estimate of epidemic optic neuropathy in The Gambia and, as such, provides an important contribution to our knowledge in identifying characteristics that may cause specific populations to be more susceptible to this public health burden.