Pharmacokinetics of topically applied cyclopentolate HCl and tropicamide

The time course of accommodative loss after the topical application of 0.5% and 1.0% concentrations of cyclopentolate HCl and tropicamide was measured over a 20-min interval in 50 age- and sex-matched subjects between 20 and 30 years of age. Computer-assisted measures of residual accommodation provided detailed data on the temporal aspects of the cycloplegia induced by these commonly utilized drugs when used alone or with the topical anesthetic proparacaine HCl. The pattern of recovery of ocular accommodation from cycloplegia was also measured over a 5-h period, starting 2 h after drug application. The results show that latency, depth of cycloplegia, and rate of accommodative loss are regulated to drug type and concentration, and are influenced by the iris coloration of the test eye. The rate of onset of cycloplegia was not accelerated in blue or brown irides by the preadministration of proparacaine. Regardless of iris pigmentation, recovery from tropicamide cycloplegia was much faster than recovery from cyclopentolate cycloplegia. In contrast, the depth of cyclopentolate cycloplegia present in brown irides during the recovery phase was much greater than in blue irides. Mechanisms to explain these observations are proposed and clinical implications of these findings are presented.