The effects of topical pilocarpine on the morphology of the outflow apparatus of the baboon (Papio cynocephalus).

The morphology of the outflow system of the baboon (Papio cynocephalus) was studied by light microscopy and transmission electron microscopy in tissue from eyes treated with topical pilocarpine. In one group of five animals the intraocular pressure (IOP) was maintained at 18 mm /g in both the experimental and the control eye of each baboon for the duration of the experiment. The endothelial meshwork was more distended, and there was a significantly greater number of giant vacuoles in the lining endothelium of Schlemm's canal in the pilocarpine-treated eyes than in the corresponding controls. However, in another series of animals, IOP was not maintained, and the differences between the treated and untreated eyes was much less striking. There appeared to be little evidence that the increase in vacuolation was produced by the direct action of pilocarpine on the endothelium of Schlemm's canal; more likely, it was a consequence of an increased passage of fluid through the drainage system. In addition, we have been able to show that (1) the mode of primary fixation can produce partial reversal of the pilocarpine effect and (2) the mechanical manipulation which is required to determine outflow facility has a deleterious effect on the morphology of the outflow tissues.