Retrocorneal pigmentation secondary to iris stromal melanocytic proliferation

A 40-year-old black man had two penetrating keratoplasties as a result of complications from alkali burns sustained many years earlier. Two further penetrating keratoplasties were performed for recurrent retrocorneal pigmentation. Both scanning and transmission electron microscopy demonstrated that the retrocorneal pigmented cells were iris melanocytes, based upon their fusiform or dendritic shapes and measurements of their cytoplasmic melanin granules. Repopulation of Descemet's membrane by the melanocytes was produced by a small remnant of atrophic iris. The pigment granules in the iris melanocytes were somewhat larger than those seen in similar cells from Caucasians or Orientals, but had identical measurements to those studied in an iridectomy specimen from another black patient. The retrocorneal iris melanocytes were able to synthesize banded basement membrane material, interrupted laminar basement membrane, and collagen fibrils. The cause of the exfoliation of the iris melanocytes onto the back of the cornea is unknown, but the discovery that iris melanocytes can proliferate in an ongoing fashion and secrete extracellular matrix provides new insight into the physiology of these cells.