Clinical and electron microscopic observations of the conjunctiva of adult patients with Bitot's spots.

Three adult patients with Bitot's spots of the conjunctiva were observed in the American Southwest; all were in good health without obvious cause for vitamin A deficiency. Serum vitamin A levels were low normal in two; the third patient was on replacement vitamin A therapy with resultant high serum levels. Serum beta-carotene levels were low in two and normal in one. Schirmer test without anesthesia was low normal in two and with topical anesthesia was abnormal in all. After 8 weeks of oral vitamin A therapy, the Schirmer test and Bitot's spots showed little response. Electron microscopy of Bitot's spots showed changes characteristic of keratinizing squamous epithelium: absence of goblet cells, increased tonofibrils, flattening of intermediate cells, loss of superficial cell nuclei, and a keratin layer. Light microscopy of the inferior cul-de-sac conjunctiva showed increased surface goblet cells in two and absence of such cells in the third; by electron microscopy the substructure of the majority of the goblet cell mucin granules had a reticulated appearance in which an electron-dense fibrillar network was present within the granule matrix. The non-mucin-containing epithelial cells of the inferior cul-de-sac for the most part appeared normal.