Visual Psychophysics / Physiological Optics - ARVO

ARVO 2013 Annual Meeting Abstracts by Scientific Section/Group – Visual Psychophysics / Physiological OpticsPurpose: The progressive age related loss of accommodation inrhesus monkeys has been studied in vivo or with in vitro mechanicalstretching to simulate disaccommodative changes in enucleated eyes(in vitro accommodation). No prior study had directly compared thetwo approaches with the same eyes. Here a direct comparison is madebetween the age-related in vivo loss of accommodation in rhesusmonkeys and in vitro mechanical stretching induceddisaccommodative changes in the same eyes after enucleation.Methods: Experiments were performed on 10 iridectomizedmonkeys aged between 10 and 25 years. Accommodation wasstimulated with intravenous (i.v.) pilocarpine and refraction measuredstatically with a Hartinger coincidence refractometer and dynamicallywith infrared photorefraction. In one subsequent i.v. pilocarpineexperiment with each monkey, accommodative changes in lensdiameter were measured dynamically. Following euthanasia one eyeeach from nine of the monkeys was dissected and stretched radiallystep-wise while measuring changes in lens focal length and diameterto attempt to achieve the largest changes possible.Results: In vivo accommodative amplitudes decreased linearly withage from 12.38 D to 3.38 D (n = 10; r 2 = 0.9097; p < 0.0001) andaccommodative decrease in lens diameter decreased linearly with agefrom 0.703 mm to 0.327 mm (n = 9; r 2 = 0.8097; p = 0.0009). In vitroaccommodative change in lens power decreased linearly with agefrom 16.9 D to 6.16 D (n = 9; r 2 = 0.8805; p = 0.0001) and in vitroaccommodative change in lens diameter decreased linearly with agefrom 1.43 mm to 0.73 mm (n = 9; r 2 = 0.62; p < 0.0009). In vitroaccommodation with the maximum radial stretch overestimated invivo accommodation on average by 2.94 ±1.604 D without opticalcompensation for ocular optical effects. In vitro accommodativechanges in lens diameter with the maximum radial stretchoverestimated the in vivo accommodative changes in lens diameter by0.65 ± 0.083 mm.Conclusions: Maximum change in power and diameter that lensesundergo with stretching overestimates the in vivo accommodativechanges in optical power and lens diameter. Both in vivo and in vitroaccommodation in the same eyes of rhesus monkeys show a similarprogressive age-related loss of accommodation. Since in vitroaccommodation does not rely on ciliary muscle function, thissupports a lenticular basis for presbyopia in rhesus monkeys.Commercial Relationships: Mark Wendt, None; Adrian Glasser,NoneSupport: NEI Core Grant P30 EY007551 to UHCOProgram Number: 4274 Poster Board Number: B0311Presentation Time: 8:30 AM - 10:15 AMAge-related loss of accommodation in rhesus monkeys isassociated with an age-related increase in lens stiffnessAdrian Glasser, Mark Wendt. College of Optometry, University ofHouston, Houston, TX.Purpose: It is generally agreed that presbyopia in humans is causedby an age-related increase in lens stiffness. Rhesus monkeys developpresbyopia with a similar relative age-course as humans and are usedas an animal model for human presbyopia, although prior studieshave suggested differences in the aetiology of presbyopia betweenhumans and monkeys. Here, the age-related loss of accommodationfrom in vivo and in vitro experiments is correlated with the stiffnessof the same lenses to ascertain the relationship between presbyopiaand lens stiffness in rhesus monkeys.Methods: Experiments were performed on 10 iridectomized rhesusmonkeys aged between 10 and 25 years. Accommodation wasstimulated with intravenous pilocarpine and refraction measured witha Hartinger and infrared photorefraction and accommodative changesin lens diameter measured with slit-lamp videography. Aftereuthanasia, one eye each from nine monkeys was used formechanical stretching experiments in which changes in lens focallength and lens diameter were measured as a function of the appliedradial stretch. Lenses were then isolated and squeezed in six 100 µmsteps while measuring the applied force.Results: In vivo accommodative amplitudes decreased linearly withage (r 2 = 0.9097; p < 0.001) and accommodative change in lensdiameter decreased linearly with age (r 2 = 0.8097; p < 0.001). Withmechanical stretching the lens power and lens diameter curves foreach lens plateaued and the maximum changes in lens power anddiameter from all lenses decreased linearly with age (r 2 = 0.8805; p