With the recognition that cases of mild, subclinical vitamin deficiency are much more common than cases of severe deficiency, the need for adequate diagnostic methods for early avitaminotic states is urgently felt by clinicians. Only by such methods can the clinician determine the borderline states of malnutrition that not only contribute to his patients' ill health but prevent the best response to therapeutic measures.
As a criterion of deficiency of vitamin A, the night blindness or dark adaptation test is valuable, especially since the work of Wald,1 Wald and Clark,2 Hecht and his co-workers3 and others has demonstrated the physiologic role of vitamin A in the generation of the visual purple. Impairment of the visual cycle occurs as one of the first signs of an inadequate supply of vitamin A.
Jeghers4 has reviewed the literature on this test, and Hecht5 has reviewed the literature on this test, and Hecht5 has
BLANCHARD EL, HARPER HA. MEASUREMENT OF VITAMIN A STATUS OF YOUNG ADULTS BY THE DARK ADAPTATION TECHNIC. Arch Intern Med (Chic). 1940;66(3):661–669. doi:10.1001/archinte.1940.00190150132009
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