The diagnosis of nutritional deficiency diseases has often been based merely on the presence of certain signs, such as conjunctival thickening, corneal vascularization, hyperkeratosis, cheilosis, glossitis, swollen and bleeding gums, petechial hemorrhages and neurological manifestations. In a recent review, Darby1 points out the danger of relying only on such physical signs and cites a number of diagnostic errors that have arisen from lack of a sound medical appraisal. Thus thickening of the conjunctiva has been used in certain surveys as an indication of chronic vitamin A deficiency. In one such study, the claim was made that 99 per cent of low income population were deficient in vitamin A and in another, that every subject examined showed changes, mostly moderate to severe, resulting from vitamin A deficiency. When these startling claims came to the attention of an experienced ophthalmologist, he pointed out that the observed conjunctival changes represent common presenile