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J.T. Siegwart, T.T. Norton, J.D. Robertson; Binocular Lens Treatment in Tree Shrews . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1984.
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Purpose: To examine lens compensation in tree shrews under binocular viewing conditions which more accurately reflect viewing conditions during normal development. Methods: Juvenile tree shrews wore a goggle frame with binocular -5D, -3D, plano, +3D, or +5D lenses (n=5 each group, except plano N=2) in their home cage without control of viewing distance. Treatment was continuous for 11 days starting 24 days after natural eyelid opening (24 days of VE). Awake, non-cycloplegic refractive state was measured daily with an autorefractor (Nidek). Cycloplegic refraction (Nidek) and A-scan ultrasonography were performed after 11 days of lens wear. Results: The responses were similar in both eyes of individual animals (values in the table are the average of the R and L eye). The -3D and -5D lenses were rapidly compensated for by an increase in axial elongation. The +3D and +5D lenses were only partially compensated for by a slowing of axial elongation and the +5D lenses produced more variable responses than the other lens powers. Interestingly, the final refractions for the -3D and -5D lenses were similar, as were the final refractions for the +3D and +5D lenses. Conclusions: Under binocular viewing conditions, with accommodation intact, and no control of viewing distance, tree shrew eyes compensate rapidly and consistently for low power minus lenses. The similar compensated refractive state for the -3D and -5D lenses may reflect active accommodation by the animals. The plus lenses appeared to slow, but did not stop axial elongation. In contrast, during recovery from an induced myopia, axial elongation ceases and eyes proceed rapidly toward their original refractive state. There may be a minimum growth rate in ‘normal’ (non-myopic) eyes. Under binocular viewing conditions that resemble viewing conditions during normal development, tree shrews eyes appear to have a stronger compensatory response when the refractive state is shifted toward hyperopia than when shifted toward myopia. View OriginalDownload SlideView OriginalDownload Slide
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