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H. M. Bossong, M. H. Swann, A. Glasser, V. E. Das; Behavioral Accommodation Measured in Strabismic Monkeys With Infrared Photorefraction. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4567.
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© ARVO (1962-2015); The Authors (2016-present)
1) To establish remote infrared photorefraction as a method for measuring accommodation in awake behaving strabismic monkeys. 2) To examine issues of photorefractor calibration specific to strabismic monkeys such as day to day variability in calibration coefficients and calibration errors due to misalignment of the photorefractor and the center of the pupil.
Data were collected from one normal and two strabismic juvenile rhesus monkeys in 15 sessions. A remote infrared photorefractor, mounted on a camera placed at a distance of 40cm, was aligned with the center of the pupil of an eye which was occluded using an infrared-pass visible block filter. Photorefraction calibration was performed by placing ophthalmic lenses (-2D to 5.5D) in front of the occluded eye while the fellow eye fixated a 2°X2° Maltese cross at 60cm. To analyze calibration errors due to misalignment between the photorefractor Purkinje image and the center of the pupil, calibrations were performed as the animal fixated the target that was placed at an eccentricity of 10° or 20° along the horizontal or vertical meridian. Analysis of the video images was performed offline in MATLAB to convert slopes of the pupil luminance profile to dioptric values.
Calibration curves were generated from the ophthalmic lenses of known power. Linear range of calibration usually extended from -1D to +4D. Calibration coefficients obtained on 5 experimental days for each monkey showed small standard deviations (straight-ahead target; slopes: N1-0.91+0.18; S1-0.67+0.14; S2-0.90+0.27) increasing confidence in the repeatability of accommodation measurements. Calibration coefficients obtained during 10° eccentric fixation, i.e., misalignment of 10° between photorefractor Purkinje image and center of pupil, was not significantly different from the 0° (straight-ahead) fixation condition (10° slopes: N1-1.02+0.10; S1-0.63+0.13; S2-0.77+0.27). Calibration coefficients obtained during 20° eccentric fixation were also similar to the other conditions tested, but the standard deviation of the slopes tended to be larger.
The infrared photorefraction technique can be reliably used to measure accommodation in awake behaving normal and strabismic monkeys. Photorefractor calibration is generally unaffected for small misalignment between the photorefractor camera and the pupil center increasing the practicality of its use in strabismic monkeys.
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