Evidence for the belief that night blindness represents the first symptom of vitamin A deficiency has been accumulating for some time.
Until recently the condition of night blindness has been considered rare in North America. Hess and Kirby,1 seeking to determine the incidence of the condition, sent questionnaires to American ophthalmologists inquiring as to the number of cases that they had identified among their patients, and all who reported stated that night blindness is uncommon. This was interpreted to mean that deficiency of vitamin A is of infrequent occurrence in North America. The later work of Jeans and Zentmire2 with the Birch-Hirschfeld visual photometer and that of Jeans, Blanchard and Zentmire3 with the biophotometer indicated that night blindness is common among children. These workers also presented evidence of vitamin A deficiency as a causative factor. Likewise the study of Park4 and of Jeghers,5 using the