Visual guidance of recovery from lens-induced myopia in tree shrews (Tupaia glis belangeri)

Academic Article

Abstract

  • Purpose: To examine, in tree shrews, the visual guidance of recovery from negative lens-induced myopia by measuring the effect of wearing low-power negative or positive lenses during recovery. To learn if removing a negative lens for 2h per day, after compensation has occurred, is sufficient to produce recovery. Methods: Starting 16days after natural eye opening (days of visual experience), juvenile tree shrews wore a monocular -5D lens for 11days to produce compensation (age-appropriate refraction while wearing the lens). Recovery in four groups was started by discontinuing -5D lens wear, which caused the treated eyes to be refractively myopic, and substituting: no lens (n=7), a plano lens (n=8), a -2D lens (n=6) or a +2D lens (n=10). In a fifth group (n=6), the -5D lens was removed for 2h each day but worn the remainder of the time. Non-cycloplegic refractive measurements were made daily for the first 10days and then less frequently. After 31-35days, the lens-guided recovery period was ended for most animals; periodic measures were continued to assess post-lens recovery changes. Results: All the eyes responded to the -5D lens and were myopic (-4.8±0.1D, mean±S.E.M.) compared to the untreated fellow control eye. In all groups except the -2D lens group, some animals exhibited slow or incomplete recovery. During recovery, the treated eye of most animals recovered until its refraction, measured with the recovery-lens in place, was near to that of the control eye. Measured without the lens, the -2D group was myopic and the +2D group was hyperopic. With the lens in place, the plano-lens, -2D lens, and +2D lens groups remained slightly myopic (-1.0±0.3D, -0.6±0.2D and -1.3±0.1D, respectively). The rate of recovery during the first four days was unrelated to the amount of myopia initially experienced by the recovering eyes. Removal of the -5D lens for 2h each day produced recovery. Conclusions: During recovery, the emmetropization mechanism uses the presence of myopia, but perhaps not the magnitude, to guide eyes toward a refractive state similar to the control eye, regardless of whether the optically-recovered eye is longer or shorter than the fellow control eye. Wearing a goggle frame containing a lens of any power limits the recovery. The recovery signal can be intermittent, present for only 2h per day, and still mediate recovery in competition with increasing amounts of hyperopia as recovery progresses. Ophthalmic & Physiological Optics © 2011 The College of Optometrists.
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    Author List

  • Amedo AO; Norton TT
  • Start Page

  • 89
  • End Page

  • 99
  • Volume

  • 32
  • Issue

  • 2