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The recent progress in the chemical identification of vitamins has brought about a demand for the clinical demonstration of early deficiency states. This has been particularly true for vitamin A. The classic deficiency state of xerophthalmia is seldom seen even in large clinics in this country. Some years ago it was shown that the power of distinguishing variations of light in persons suffering from lack of vitamin A was inferior to the power in individuals on a normal diet. Early investigations were concerned with the determinations of the sensibility of the eye to light of different intensity by measuring the minimum visible. This demonstrated faulty adjustment to darkness and improvement with administration of vitamin A. Later photometric tests were devised. This monograph takes up the historical development of this approach and gives a critical evaluation of the various methods employed. The authors present in detail the method they have employed
On Deficiency of A Vitamin and Visual Dysaptation. JAMA. 1937;109(1):73. doi:10.1001/jama.1937.02780270075028