FINE-STRUCTURE AND SIGNIFICANCE OF SNAKE-LIKE CHROMATIN CONJUNCTIVAL EPITHELIAL-CELLS

Purpose. In patients with several disorders of the ocular surface, in wearers of contact lenses, and occasionally in patients considered ''n ormal,'' the epithelial cells of the bulbar conjunctiva present in the ir nucleus peculiar alterations of the heterochromatin arrangement tha t, because of the shape this assumes, are named ''snakelike chromatin, '' or ''snakes.'' To obtain some information about the yet unknown eti ology of these snakes, the authors investigated them by electron micro scopy. Methods. Identical conjunctival epithelial cells, collected by impression cytology from longtime contact lens wearers, were first ide ntified by light microscopy and then observed by scanning and transmis sion electron microscopy. Results. In scanning electron microscopy, cy toplasmic and nuclear components of air-dried cells were seen collapse d on the snake, which became pr-eminent at the surface, proving its hi gh degree of compactness and showing its axial position and characteri stic shape in the elongated nucleus. In transmission electron microsco py, the marginal heterochromatin of the affected nuclei was detached p eripherally, forming thin chromatin strands directed toward the main n uclear axis and accumulating there into the snake structure. An import ant component of the nuclear skeleton, the fibrous lamina, was altered or lost, whereas the nuclear envelope itself did not move and remaine d intact. Stages of the snake alteration considered as advanced showed an almost completely reversed eu- and heterochromatin distribution, a nd nucleoli were usually no longer seen. In cases with increased epith elial alteration, there occurred various stages of segmentation of nuc lei, induced by an atypical accumulation of cytoplasmic filaments, rol ling up around the nucleus and constricting it like a cuff. Conclusion s. The presence of a mechanical stimulus is shown in the ultrastructur al findings, and these strongly suggest that it is altering the nuclea r and cytoplasmic skeleton, producing snakes and their segmentation. T herefore, snakelike chromatin is suggested as an indicator of mechanic al stress on the ocular surface.