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Clinical Sciences
November 1, 2005

Bimatoprost-Induced Periocular Skin Hyperpigmentation: Histopathological Study

Author Affiliations

Author Affiliations: Department of Ophthalmology and Visual Sciences, University of Illinois, Chicago (Drs Kapur, Osmanovic, Toyran, and Edward); and Arlington Eye Physicians, Arlington Heights, Ill (Dr Osmanovic).

Arch Ophthalmol. 2005;123(11):1541-1546. doi:10.1001/archopht.123.11.1541

Objective  To investigate light microscopic and ultrastructural changes in bimatoprost-induced skin hyperpigmentation.

Methods  Eyelid biopsy specimens from bimatoprost-treated patients and matched controls were examined by light microscopy and transmission electron microscopy. Using an image analyzer, melanin granules were counted on Fontana-Masson–stained sections, and melanosomes were counted on electron micrographs. Immunohistochemical analysis was performed with antibodies against S100 and CD3. Positively labeled cells were counted.

Results  By light microscopy, a marked increase in the number of melanin granules was noted in the bimatoprost-treated specimens. Electron microscopy demonstrated dermal melanocytes with prominent rough endoplasmic reticulum and abundant normal-sized melanosomes in different stages of maturation as compared with control specimens. Furthermore, the keratinocytes of the bimatoprost-treated specimens showed abundant mature melanosomes when compared with controls. Also of note, atypical melanocytes were absent in both specimens. The S100-positive melanocytes were comparable in bimatoprost-treated and control specimens. Few CD3- and CD68-positive cells in the bimatoprost-treated specimens were noted in both groups.

Conclusion  Bimatoprost-induced periocular hyperpigmentation is caused by increased melanogenesis. There was no evidence of melanocyte proliferation or prostaglandin-induced inflammation in the specimens that were examined.