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D. Troilo, E. Harb, K. Totonelly, L. Merriwether, D. Bradley; Accommodation Behavior in Rhesus Macaques During Free Viewing of an Operant Conditioned Visual Task . Invest. Ophthalmol. Vis. Sci. 2005;46(13):715.
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Purpose: There is much interest in the relationship between near visual experience, accommodation, and the development of myopia. Because the state of accommodation changes retinal image focus, a factor involved in the control of eye growth and refractive state, we have been interested in quantifying accommodative behavior under experimental and natural conditions that can affect the development of refraction. In this study we examine accommodative behavior during an operant conditioned near point visual task in primates. Methods: Three adult rhesus macaques were trained to perform a visual match–to–sample task that required the monkey to look at a video display while manipulating a cursor with a joy stick to indicate a response. The monkeys were trained to look at the monitor binocularly through a mask integrated into the testing cage so that while performing the task their accommodative behavior could be measured using an infrared video photorefractor (PowerRefractor, MultiChannel Systems). Refractions and eye position were recorded throughout several testing sessions at several working distances (20–60 cm). Results: Refractions measured while the monkeys were actively on task indicate that the accommodative response was variable, but on average responsive to the stimulus demands. The standard deviations of the mean accommodative responses ranged from ±0.5 to ±2.2 D, and were significantly greater at the closer working distances (ANOVA, p<0.05). Accommodation stimulus–response functions show that, on average, the monkeys accommodate to the monitor at all working distances tested (average slope = 0.989 ±0.162). The mean accommodative lag was 0.78 ±0.41 D. Examination of the distribution of refractions shows both normal and binomial distributions. The binomial distributions are peaked near the stimulus demand and the subject's distance refraction. Conclusions: These data suggest that accommodative responses in primates trained to perform a complex visual discrimination task, while on–average accurate, are quite variable. This variability in the accommodative response to near visual demands is a factor to consider in the temporal integration of retinal defocus that may affect the visual control of eye growth.
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