The tremendous increase in the sensitivity of the retina when it is kept in the dark for a prolonged period is common knowledge, and the quantitative measurement of this phenomenon is not new. It is also well known that certain pathologic conditions may affect this process of dark adaptation and give rise to varying degrees of night blindness. However, it has been only within the past decade that the knowledge of this fundamental principle has aroused widespread interest. The impetus was given by the realization that in certain metabolic disorders the course of the dark adaptation and final threshold (minimum light visible after a prolonged period in the dark) was altered.
These various metabolic disorders were linked to vitamin A deficiency by numerous investigators working in separate fields. The recognition of vitamin A as one of the products of decomposition of visual purple when acted on by light and its
McDONALD R, ADLER FH. EFFECT OF ANOXEMIA ON THE DARK ADAPTATION OF THE NORMAL AND OF THE VITAMIN A-DEFICIENT SUBJECT. Arch Ophthalmol. 1939;22(6):980–988. doi:https://doi.org/10.1001/archopht.1939.00860120052004
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