Aging effects on accommodation and outflow facility responses to pilocarpine in humans
M. A. Croft, M. J. Oyen, S. J. Gange, M. R. Fisher and P. L. Kaufman
Department of Ophthalmology and Visual Sciences, University of Wisconsin Medical School, Madison, USA.
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-microL 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.
