Morphologic studies to date show that prostanoid-induced iris color change is not associated with any major pathologic process in the tissue. There is no evidence of melanocyte proliferation. The most likely mechanism for iris color darkening is increased melanogenesis, but this is not so marked as to cause any extensive release of melanin granules that might cause iris inflammation or even a pigmentary-type of glaucoma. Some patients, but not all, with color darkening have an apparent thickening of the anterior border zone; it remains to be established whether this is true thickening or merely if the anterior border is emphasized because of increased pigmentation.
*Unit of Ophthalmology, Department of Medicine, University of Liverpool, Liverpool, England, and †Department of Ophthalmology, Johannes Gutenberg-Universität Klinikum, Mainz, Germany.
Correspondence to Ian Grierson, PhD, Unit of Ophthalmology, Department of Medicine, University of Liverpool, University Clinical Departments, Duncan Building, Daulby St. Liverpool L3 9PF United Kingdom; e-mail: firstname.lastname@example.org