Ocular surface squamous neoplasia (OSSN). A, Clinical appearance. Note the “corkscrew” vascular pattern of the conjunctival portion and gelatinous appearance with focal leukoplakia of the corneal portion. Also note feeder vessels. B, Histologic examination shows the sharp demarcation (arrow) between normal and abnormal epithelium in OSSN. The epithelium is hyperplastic, with surface keratinization (K). As the basement membrane is intact, a diagnosis of conjunctival intraepithelial neoplasia (CIN) is made. There is a chronic inflammatory response in the stroma (CI). Also note areas of elastotic degeneration in the stroma (arrowheads), indicating that the lesion arose over a pinguecula. C, High magnification (different patient) shows the transition zone where neoplasia begins (arrow). To the right of the arrow, the epithelium exhibits mild keratinization, hyperplasia, nuclear hyperchromasia and pleomorphism, goblet cell loss, altered cell polarity, full-thickness involvement, and mitotic figures (M). The basement membrane is intact (arrowheads). D, In squamous cell carcinoma, tongues of epithelium violate the basement membrane and invade the stroma (arrows), with squamous eddies (arrowheads). E, Gross photograph of squamous carcinoma that has invaded the limbus and anterior chamber angle through a previous surgical incision (arrow).