Spontaneous intrastromal iris cyst. A case report with immunohistochemical and ultrastructural observations.

A 39-year-old man had an enlarging intrastromal iris cyst that obstructed the chamber angle inferotemporally and abutted the cornea. No history of ocular trauma or previous surgery was present. Iridocyclectomy with en bloc resection of the cyst was performed. The cyst was lined by one to three cell layers of focally pigmented epithelium that ultrastructurally exhibited desmosomes, tonofilaments, terminal bars, and apical microvilli. Additionally, membrane-bound melanin granules (melanosomal complexes) consistent with phagocytized uveal melanin granules were observed. Immunohistochemistry confirmed intracellular keratin. We conclude that the non-traumatic cyst reported herein is of surface ectodermal origin and suggest that such cysts be removed en bloc by sector iridectomy or iridocyclectomy if the lesion has been proven to enlarge.