Inhibitors of surgically induced miosis

Miosis induced by surgical trauma is a frequent problem during extracapsular cataract surgery. In experimental surgery on rabbits, the inhibitory effect on pupillary constriction of cyclo-oxygenase inhibitors, local anesthetics, capsaicin (presumed substance P depletor), sympathomimetic agents, and anticholinergic agents were studied. In eyes predilated with tropicamide, iris massage caused marked pupillary constriction. Randomized pretreatment with the following agents significantly inhibited miosis: flurbiprofen, P less than 0.005; topical anesthetics (benoxinate, P less than 0.001, cocaine, P less than 0.05, proparacaine, P less than 0.005); and retrobulbar capsaicin, P less than 0.005. No significant inhibition was shown with topical indomethacin aqueous solution (P less than 0.15), topical tetracaine (P less than 0.15), or retrobulbar lidocaine (P less than 0.15). No single agent or combination of agents blocked the total miotic response; however, a combination of flurbiprofen, benoxinate, and capsaicin blocked more than two third of the miosis. Phenylephrine, a sympathomimetic (active) mydriatic agent, was more effective than anticholinergic (passive) mydriatic agents in obtaining maximal pupillary size after surgical iris massage.