The fine structure of chromatin alterations in conjunctival epithelial cells in keratoconjunctivitis sicca

To study the ultrastructure of nuclear chromatin changes of conjunctival epithelial cells in imprints of dry-eye patients.

Imprints with nuclear chromatin changes of the conjunctival epithelium from dry-eye patients were first selected by light microscopy (LM). The latter allowed processing material with special interest (chromatin changes) for electron microscopy (EM). Ultrathin sections were cut tangential to the filter surface to obtain an large overview of the collected imprints. For scanning electron microscopy (SEM), selected specimens were dehydrated in ethanol and dried by the critical-point method or in some cases only air-dried. As controls, imprints of healthy patients were used.

EM of the control samples showed sheets of well-preserved conjunctival nongoblet epithelial cells and goblet cells filled with secretory granules. Intercellular processes contributed to the formation of a cohesive sheet of epithelial cells. In dry-eye patients, signs of squamous metaplasia such as enlargement of nongoblet epithelial cells, increased keratinization, and nuclear chromatin changes were disclosed. The goblet cell density was drastically reduced or lost. Nuclear chromatin changes showed a pathologic distribution of eu- and heterochromatin, resulting in an axial snake- or stick-like chromatin condensation. Intracellular filament-like structures were identified in severe cases to cause a segmentation of nuclei.

The fine structure of cellular and nuclear changes occurring in KCS are shown in detail. The data are in line with EM observations of impression cytology of contact lens wearers, thus confirming the ubiquitous origin of squamous metaplasia and authenticity of the snake phenomenon in squamous metaplasia. Potential pathomechanisms that might be involved in the development of chromatin alterations in conjunctival epithelial cells undergoing squamous metaplasia are discussed.