The toxic effects of pilocarpine gel and drops on rabbit cornea

Pilocarpine drops and gel were applied daily for 3 months to rabbit cornea to determine their cytotoxic effects. The corneas were examined clinically with slit lamp biomicroscopy and histologically with scanning and transmission electron microscopy. The gel-treated corneas developed edema and desquamation of the superficial epithelial layers. Vacuoles, swollen mitochondria and amorphous deposits were detected in the basal epithelial layers. The drop-treated corneas developed endothelial cell damage characterised by cytoplasmic vacuoles, swelling and degeneration of the intracellular organelles. The study confirms the clinical impression that pilocarpine gel can produce anterior corneal damage. The toxic effect of pilocarpine gel on the corneal endothelium was much less than the effect produced with pilocarpine drops.