Melanin in the Trabecular Meshwork is associated with Age, POAG but not latanoprost treatment.

Abstract

Abstract: : Purpose:The trabecular meshwork is known to become pigmented by phagocytosis of iris–derived melanin granules present within the circulating aqueous humor. We wished to determine the distribution of melanin with age and POAG and also see if there was an association with latanoprost treatment. Methods:Trabeculectomies (25) taken from normal enucleated eyes over forty years and conventional surgical trabeculectomies (62) from Caucasians were selected on the basis of macroscopic examination for the presence of Schlemm’s canal and a substantive portion of meshwork. Quantitative, masked light and electron microscopic analysis was conducted on each. Results:The percentage of melanin containing meshwork cell profiles in the control group was 12.9% whereas the incidence in the POAG group was significantly (P<0.01) higher at 33.2%. Comparison of POAGs that had not been on latanoprost (50) against those that had (12) showed no significant difference although only 6 of the latter had evidence of iris darkening at the time of surgery. Electron microscopy confirmed that the melanin granules were mostly intracellular and of the larger iris epithelial type even in the latanoprost–treated specimens. Conclusions:Meshwork pigmentation was shown to be due to iris epithelial melanin and not iris stromal melanin even in latanoprost treated cases. POAG is associated with increased meshwork pigmentation by a mechanism yet unknown but one that is unlikely to be influenced by prostanoid drugs.

Keywords: pathology: human • trabecular meshwork • drug toxicity/drug effects