The Relation Between Vitamin a and Dark Adaptation

I. PURPOSE Night blindness and similar visual disturbances have long been associated with the nutritional state of the body. In recent years this connection has been traced to the vitamin A of the diet¹and has become understandable in terms of the chemical relation between vitamin A and the light-sensitive pigments of the retina.² After the establishment of vitamin A as a factor in the visual cycle, it seemed logical to use the properties of vision for the detection of early stages in vitamin A deprivation. Such tests were made by Edmund and Clemmesen³with visual intensity discrimination as an index and by Jeans and Zentmire⁴with dark adaptation as a criterion. Other investigations⁵followed and, though some of this work has been found to be perhaps more enthusiastic than critical,⁶it showed that the original idea is probably sound and that under properly