History of nightblindness: a simple tool for xerophthalmia screening.

Among 5925 preschool-age children examined in a house to house rural field study, X1B (Bitot's spot with xerosis) and/or an history of nightblindness (XN) was presented in 325. Mean serum vitamin A levels among those with isolated XN (13.9 microgram/dl), isolated X1B (13.4 micrograms/dl), and coexistent XN/X1B (12.1 microgram/dl) were similar, and significantly below that of normal age/sex/neighborhood matched controls (17.6, 17.1, and 18.3 microgram/dl, respectively). The mean serum vitamin A level of the matched controls was significantly below that of normal, randomly sampled children from the study population as a whole (20.6 microgarm/dl). As independent screening criteria, disregarding the presence of absence of other signs, twice as many children had a history of XN as had X1B (84 and 41% of all clinically abnormal children, respectively). Of randomly sampled children 55% but only 15% of cases of XN had serum vitamin A levels above 20 microgram/dl. Of children with a history of nightblindness 97% had impaired scotopic vision on objective testing, but the mean serum vitamin A levels among test positives and negatives were identical. These results suggest a properly eleicited history of nightblindness can be almost as specific and far more sensitive an index of vitamin A deficiency and early xerophthalmia than the prescence of Bitot's spots (X1B), and that vitamin A deficiency is a clustered, neighborhood phenomenon rather than an isolated, sporadic occurrence.