Histology and transmission electron microscopy of the cornea in xeroderma pigmentosum type C.

Xeroderma pigmentosum is a very rare precancerous skin disease that is triggered by sunlight. It is caused by a defect in the DNA repair system and causes benign and malignant transformations. Only eye tissues that come into contact with UV light are affected, such as the lids, conjunctiva and cornea. We describe a patient who suffered from xeroderma pigmentosum type C, showing the typical skin alterations but no sign of malignancy. A perforating keratoplasty was performed on both eyes because of the dense opacity of the corneas. The corneal buttons obtained were examined by light and transmission electron microscopy. Degeneration was found only in the basal-cell layer of the corneal epithelium. The most severe morphological changes were seen in Bowman's layer, the subepithelial stroma, Descemet's membrane and the corneal epithelium. Bowman's layer was often interrupted or replaced by a degenerative pannus, which extended into the underlaying stroma. Subepithelial "channels" were localized in the basal epithelium and protruded into the subepithelial stroma. In both corneas, Descemet's membrane contained different amounts of so-called lattice collagen, and the remaining endothelial cells in the left cornea contained numerous melanin granules.