Aging effects on accommodation and outflow facility responses to pilocarpine in humans

Objective: To determine the relationships among age, outflow facility, and refractive and facility responses to pilocarpine in humans. Methods: Refraction, intraocular pressure, and outflow facility were determined in 30 normal volunteers aged 20 to 75 years, by coincidence refractometry, applanation tonometry, and Schiotz tonography, respectively, before and 1 hour after a 30-mu L drop of 2% or 6% pilocarpine. Simple regression of baseline facility, postpilocarpine facility, and facility change, on age and refractive change singly and jointly, was performed. Stepwise regression models and graphic conditioning plots were used to determine, for each facility variable, its relationship to age or refractive change specifically. Results: Baseline outflow facility and maximum pilocarpine-induced refractive change (ie, accommodation) declined with age, but the decrease in intraocular pressure and the facility response to pilocarpine did not. After adjusting for age, for baseline facility, there was no further relationship to 6% pilocarpine-induced accommodation, and a slight residual relationship to 2% pilocarpine-induced accommodation. After adjusting for both 2% or 6% pilocarpine-induced accommodation, the relationship to age was still significant. The facility increase after 2% or 6% pilocarpine did not depend on age and/or accommodative amplitude. Conclusions: In humans, as previously described in rhesus monkeys, an age-related loss of ciliary muscle mobility may compromise the basal function of the trabecular meshwork. However, unlike monkeys, humans exhibit no loss of the intraocular pressure or outflow facility response to pilocarpine with age.