Comparison between in vivo and in vitro age-related loss of accommodation in rhesus monkeys

Abstract

Purpose: The progressive age related loss of accommodation in rhesus monkeys has been studied in vivo or with in vitro mechanical stretching to simulate disaccommodative changes in enucleated eyes (in vitro accommodation). No prior study had directly compared the two approaches with the same eyes. Here a direct comparison is made between the age-related in vivo loss of accommodation in rhesus monkeys and in vitro mechanical stretching induced disaccommodative changes in the same eyes after enucleation.

Methods: Experiments were performed on 10 iridectomized monkeys aged between 10 and 25 years. Accommodation was stimulated with intravenous (i.v.) pilocarpine and refraction measured statically with a Hartinger coincidence refractometer and dynamically with infrared photorefraction. In one subsequent i.v. pilocarpine experiment with each monkey, accommodative changes in lens diameter were measured dynamically. Following euthanasia one eye each from nine of the monkeys was dissected and stretched radially step-wise while measuring changes in lens focal length and diameter to attempt to achieve the largest changes possible.

Results: In vivo accommodative amplitudes decreased linearly with age from 12.38 D to 3.38 D (n = 10; r² = 0.9097; p < 0.0001) and accommodative decrease in lens diameter decreased linearly with age from 0.703 mm to 0.327 mm (n = 9; r² = 0.8097; p = 0.0009). In vitro accommodative change in lens power decreased linearly with age from 16.9 D to 6.16 D (n = 9; r² = 0.8805; p = 0.0001) and in vitro accommodative change in lens diameter decreased linearly with age from 1.43 mm to 0.73 mm (n = 9; r² = 0.62; p < 0.0009). In vitro accommodation with the maximum radial stretch overestimated in vivo accommodation on average by 2.94 ±1.604 D without optical compensation for ocular optical effects. In vitro accommodative changes in lens diameter with the maximum radial stretch overestimated the in vivo accommodative changes in lens diameter by 0.65 ± 0.083 mm.

Conclusions: Maximum change in power and diameter that lenses undergo with stretching overestimates the in vivo accommodative changes in optical power and lens diameter. Both in vivo and in vitro accommodation in the same eyes of rhesus monkeys show a similar progressive age-related loss of accommodation. Since in vitro accommodation does not rely on ciliary muscle function, this supports a lenticular basis for presbyopia in rhesus monkeys.

Keywords: 404 accommodation • 653 presbyopia