Echothiophate-induced structural alterations in the anterior chamber angle of the cynomolgus monkey.

Four cynomolgus monkeys were treated topically twice daily in one eye with echothiophate iodide (PI) doses of 63, 75, or 250 micrograms per treatment for 7.7 weeks to 7 months. The opposite eyes of two monkeys received a control solution (diluent). The anterior ocular segments of all six eyes were studied by light and transmission electron microscopy during treatment. In the PI-treated eyes, the cribriform and outer corneoscleral meshwork were unusually dense. The trabecular meshwork was collapsed and the lamellae showed thickened basement membranes and thickened sheaths of elastic-like material. Most endothelial cells were enlarged and activated. Some contained many glycogen particles; others showed evidence of degeneration. The cribriform meshwork contained much more extracellular fine fibrillar material than normal, and the endothelium of the inner wall of Schlemm's canal was damaged. The PI-contracted ciliary muscle had a more rectangular shape than normally contracted muscles, and the inner edge extended so far anteriorly that in some areas it overlapped and occluded the trabecular meshwork. The muscle cells appeared damaged, and their basement membranes were thickened. The nonpigmented epithelial cells of the ciliary processes showed signs of degeneration, and within the pars plana some contained large, weakly osmiophilic inclusions. The basement membrane of the ciliary epithelium was thickened everywhere. The stromal vessels of the pars plana were dilated, and signs of inflammation were present. The sphincter iridis was damaged and there were iridocorneal adhesions. The 5 month diluent-treated eye demonstrated mild structural abnormalities in the meshwork.