Latanoprost-induced iris darkening: a morphometric study of human peripheral iridectomies

Abstract

This study compared the melanocytes of peripheral iridectomy specimens from two eyes that had latanoprost-induced iris darkening (LIID) with iridectomies from the fellow untreated eyes. Two patients were with LIID were identified in a series of 17 patients requiring bilateral trabeculectomy. The first trabeculectomy procedure provided a control peripheral iridectomy for each patient, whereas the second eye was treated with once daily 50 μg/ml latanoprost drops for 6 months. The four peripheral iridectomy specimens from the two LIID patients were subjected to quantitative morphometric analysis by light microscopy of iris cellularity, and electron microscopy of iris melanocyte immature melanosomes and mature melanin pigment granules. There was no significant difference in stromal cellularity between the LIIDs and their respective controls, nor were there significant differences in the numbers of immature melanosomes or melanin granules in the melanocytes. However, there was a significant increase in the diameter of melanin granules that was more pronounced in the anterior border layer than the deeper stroma. With the anterior border melanocytes, the increase in melanin granule size was associated with significant increases in granule area and the percentage of cell cytoplasm occupied by melanin (granularity). The only morphologic change identified in two peripheral iridectomies that had LIID when compared to untreated fellow eye specimens was a modest increase in the size of stromal melanocyte melanin granules that were pronounced in the cells of the anterior border layer.—Hans E. Grossniklaus