Purpose: To investigate the histopathologic causes for the most prominent clinical observations of the iris of patients with pseudoexfoliation syndrome (PXS), particularly poor mydriasis but also atrophy of the iris pigment epithelium with anterior chamber melanin dispersion, stromal atrophy, and vascular changes.
Methods: Thirty-three iris specimens from patients with PXS with and without glaucoma were investigated by transmission electron microscopy with special regard to sphincter and dilator muscle tissues.
Results: Pseudoexfoliation fibers were observed consistently in association with fibroblasts and melanocytes in the iris stroma, endothelial cells and pericytes of vessels, both anterior and posterior pigment epithelial cells, and muscle cells of sphincter and dilator muscles. The various cell types showed uniformly surface cell membrane excavations with PXS fibers, indicating local PXS production. Focal disintegration of the pigment epithelial layers was associated with unusual PXS material aggregations along the apical aspects of epithelial cells. Compared with age-matched control specimens, the muscle cells showed, in addition to PXS production, remarkable degenerative and atrophic changes in PXS eyes.
Conclusion: The authors suggest that abnormal extracellular matrix production and/or vascular abnormalities leading to tissue hypoxia cause degenerative tissue changes and that atrophy of muscle cells might potentiate the reduction of dilating properties of the iris.