Presbyopia, the age-dependent decline in accommodative amplitude, clinically afflicts every individual reaching the age of 40 to 45 years. Various pathophysiologic mechanisms have been proposed, but none is proven, and until now no animal model for their study has existed. Refraction, axial dimensions, and pharmacologically-induced accommodation were determined in caged rhesus monkeys aged 0.5 to 32 years. Accommodative amplitude decline in an age-dependent manner from greater than 40 diopters to 0 diopters. Mean accommodative amplitude in 0.5 to 5-year old animals was 34.4 diopters; in greater than 25-year old animals it was 5 diopters. Considering the relative life expectancy and accommodative amplitude of rhesus and human, the rate of the age-dependent decline in accommodation was remarkably similar in the two species, as were the relationships between resting axial lenticular thickness and age, and between drug-induced accommodative amplitude and change in lenticular thickness. Thus, the rhesus monkey appears to provide the first known animal model for the study of accommodation and presbyopia as they occur in the human.