Outflow facility and its response to pilocarpine decline in aging rhesus monkeys

Refractive error and total outflow facility were determined by Hartinger coincidence refractometry and two-level constant-pressure perfusion, respectively, in 17 rhesus monkeys, aged 5 to 29 years. Maximum accommodative response to corneal (iontophoretic) carbachol hydrochloride, baseline outflow facility, and the facility response to strong but submaximal intracameral doses of pilocarpine hydrochloride all declined with age. The correlation between accommodative response to carbachol and facility response to pilocarpine was slightly stronger than that between age and facility response. Since the ciliary muscle plays a major role in controlling both outflow facility and accommodation, and since histologic and videographic techniques demonstrate an age-related decline in rhesus ciliary muscle excursion induced by topical pilocarpine or electrical stimulation of the Edinger-Westphal nucleus, the present data support the hypothesis that an age-related decline in ciliary muscle mobility is associated, perhaps causally, with an age-related decline in facility and facility responsiveness to cholinergic drugs.