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DV Bradley, EL Smith, RS Harwerth, A Fernandes; A Nearwork-induced Myopic Shift, Without Sustained Accommodation, In Primates . Invest. Ophthalmol. Vis. Sci. 2002;43(13):194.
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Purpose: Human studies have long shown a relationship between prolonged performance of certain nearwork tasks and the development of myopia. Until now, however, there has only been indirect evidence of a causal link. In the present report we introduce an animal model that was used to investigate the relationship between nearwork and myopia. Methods: Adolescent rhesus monkeys performed computer-based visual tasks for at least 2 yrs. The 3 experimental conditions were: a) a detection task at far (∼114 cm, 60 min/d, N = 9); b) a simple discrimination task at near (∼25 cm, 45 min/d, N = 3); and c) a complex discrimination task at near (20 cm, viewing through +5 D lenses, 120 min/d, N = 4). Measurements of refractive error (RE), via cycloplegic retinoscopy, were obtained at regular intervals. Results: Age-matched monkeys with no exposure to visual tasks (normal controls, 4-6 yrs old, N = 30) had a stable, mean RE of +2 D. Monkeys that performed the visual task at far exhibited a fairly stable mean RE of 0.48 D. Both groups of monkeys that worked on near tasks, however, exhibited a progressive change in RE. Monkeys that worked on the simple task at near underwent a myopic shift relative to normal controls that resulted in a mean absolute RE of 0.25 D. Most of the monkeys in the complex task at near exhibited an even greater myopic shift, which resulted in a mean absolute RE of -3.25 D. While the monkeys on the complex near task had accommodation neutralized via spectacle lenses, preliminary IR videoretinoscopy assessments showed that monkeys on the simple near task engaged accommodation for only a small portion of each trial. Conclusion: These data provide direct evidence that a myopic shift can be induced by the performance of near visual discrimination tasks in primates. These results also indicate that sustained accommodation is not the mechanism for the present myopic shift. Because monkeys can be trained to perform these visual discrimination tasks, they are an ideal animal model to investigate the mechanisms involved in the development of myopia associated with nearwork.
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