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Lin He, Mark Wendt, Adrian Glasser; Accommodation In Rhesus Monkeys Measured By Full-field Infrared Photorefraction. Invest. Ophthalmol. Vis. Sci. 2011;52(14):828.
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Interest has grown in understanding the relationship between peripheral refraction and accommodation. Photorefraction has been used to measure full-field refraction in humans. Here, a new approach has been developed to measure full-field refraction and accommodation in anesthetized rhesus monkeys.
To do full-field photorefraction, a camera positioned 30 cm in front of the eye was attached to a rod that was rotated in a horizontal arc with the eye at the center of curvature of the arc. A potentiometer with a DC power supply was attached to the pivot point of the rod so the potentiometer resistance changed proportionally with the angle. The analog output from the potentiometer enabled dynamic recording of the angle of rotation through an A/D converter. A real-time Matlab application was developed to acquire and analyze photorefraction images and simultaneously measure the rotation angle at 30 Hz. Full-field, trial-lens photorefraction calibrations were compared with on-axis calibrations. In six monkeys (including two repeats of one monkey) (ages: 11.3 to 13.6 y, mean±SD: 12.8±0.9 y) full-field refraction measurements were performed before and during carbachol iontophoresis stimulated accommodation.
The Matlab photorefraction application had less than 0.1 D of variance and allowed eccentricity measurements with angular resolution of 0.1°. Photorefraction of the monkey eyes was measureable from at least -30º to 30º over 20 seconds. In five monkeys that showed linear calibration functions (r2>0.85), the full-field calibration was mostly consistent with on-axis calibration, but at some eccentricities for some eyes, the calibrated slopes either increased by up to 2% or decreased by up to 25%. On axis accommodative responses ranged from 5.82 D to 14.30 D (mean±SD: 9.14±3.96 D). Within the 60º field, the off-axis accommodative responses varied from the on-axis response by -1.17±2.02 D to +3.07±2.85 D. Relative to the on-axis accommodation, temporal retinal fields tended to have larger accommodation changes (mean=3.07 D) compared to the nasal fields (mean=0.77 D).
This system is capable of reliably measuring dynamic, full-field refraction reproducibly in anesthetized monkeys. The drug stimulated accommodative response was relatively uniform across the central 10° visual field, but varied more peripherally and non-symmetrically between nasal and temporal fields.
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