Basal cells of the corneal epithelium in man and monkey. Variation in morphology associated with fixation procedures.

Abstract

The cellular nature of the corneal epithelium was first described by van Leeuwenhoeck (i 693-i78), and it is now generally believed by workers who have carried out morphological studies that cells of an uncertain nature occur in the basal region of the corneal epithelium. Ranvier (I88I) described "wandering cells" that had migrated from blood vessels, but it was Virchow (i91o) who first observed that some cells appeared darker than others apparently because of compression of the cytoplasm. A different view, however, was held by Egorow (I934), who believed them to be homologous with similar cells in the mammalian epidermis, and hence called them Langerhans cells. Binder (I 951, I 952) described clear "matrix cells", which remained permanently in the basal layer and which divided to give rise to young cells which were compressed forwards into the epithelium. Cogan (I951), however, stated that the dark cells probably represented the more mature basal cells which were in the process of migrating forwards.The use of different techniques appears to have produced conflicting results. By staining with silver carbonate, Scharenberg (I955) was able to demonstrate "polymorph elemients" which penetrated the epithelium and were intimately connected with the nerves, while Pau and Conrads (I 957), using a similar technique, came to the conclusion that the so-called Langerhans cells were associated with nerve fibres and hence were analogous to Schwann cells.The first electron microscopical study was carried out by Jakus ( 1 954) on the rat cornea. She described finger-shaped processes on the surfaces of the basal cells, and these were subsequently named "basal layer branched cells" by Whitear (i960), who studied the mouse cornea electron mricroscopically and suggested that these cells were associated with the transport of metabolites. This was followed by an account of the rabbit cornea by Teng (I96I), who a year later (Teng, I962) described the human cornea. Because of the increased endoplasmic reticulum and tonofibril elements and the presence of osmophilic granules, he suggested that the more electron dense cells should be called "secretory epithelial cells", since he believed that their apocrine secretion contributed to the formation of the basement membrane. He observed that these cells, usually few in number, increased in pathological conditions for reasons which were not fully understood at that time.