—Xerophthalmia ("dry inflamed eye") refers to clinically detectable disease.1-4 As defined by the World Health Organization1-3 and the International Vitamin A Consultative Group4 nightblindness (XN), conjunctival xerosis (X1A), and Bitot's spots (X1B) represent early, mild xerophthalmia, in contrast to corneal xerosis (X2) and, particularly, destructive corneal melting (X3).Early "vitamin A deficiency" is another matter, and one that is difficult to define. The work of Wolbach et al,5 Mori,6 and Blackfan et al7 suggest squamous metaplasia of the respiratory and genitourinary tracts may well precede xerophthalmia. More sophisticated probes of cellular metabolism and immunologic status would likely identify earlier, milder consequences of vitamin A deficiency. Except when severely depressed, serum vitamin A levels are not a reliable index of either vitamin A stores or their consequences.We viewed impression cytology as one potential approach to the objective determination of physiologically significant vitamin
Sommer A, Wittpenn J. Early Detection of Xerophthalmia by Impression Cytology-Reply. Arch Ophthalmol. 1986;104(7):971–972. doi:10.1001/archopht.1986.01050190028007
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