Inhibition of pilocarpine-induced aqueous humor flare, hypotony, and miosis by topical administration of anti-inflammatory and anesthetic drugs to dogs

Abstract

Objective - To investigate the mechanism by which pilocarpine causes increased aqueous humor (AH) flare, hypotony, and miosis in dogs. Animals - 6 dogs with normal eyes. Procedure - Both eyes of each dog were treated topically with a 2% solution of pilocarpine, and 1 eye of each dog was additionally treated with commercially available ophthalmic solutions. Breakdown of the blood-aqueous barrier (BAB) was quantitated in each eye, using laser flaremetry to measure AH flare. Intraocular pressure and pupil size were also measured. Results - Pilocarpine caused increased flare from BAB breakdown that was inhibited by the drugs tested. Inhibition (most to least) of BAB breakdown was flurbiprofen more than diclofenac, proparacaine, or suprofen, which were more than 0.125 or 1.0% prednisolone. Inhibition appeared dose-dependent and caused consensual inhibition in the contralateral eye. Intraocular pressure was decreased only in proparacaine-treated eyes and increased in eyes treated with nonsteroidal anti-inflammatory drugs (NSAID). Flurbiprofen and proparacaine were the most effective at blocking miosis. Conclusions - Pilocarpine produced a predictable, reproducible BAB breakdown in dogs. Miosis and increased AH flare were inhibited equally by proparacaine or NSAID, suggesting that these signs were caused by neuropeptide release into the AH from antidromic stimulation, which subsequently triggers prostaglandin production. Hypotony was inhibited only by anti-inflammatory drugs. Clinical Relevance - Proparacaine in combination with pilocarpine would be the best choice for treating dogs with acute glaucoma. Topical administration of NSAID should not be used to treat dogs with acute glaucoma, because they increase intraocular pressure and negate the effects of pilocarpine.