May 2007
Volume 48, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2007
Similarities Between Myopia Induced in Tree Shrews With Form Deprivation, Minus Lenses, and Darkness
Author Affiliations & Notes
  • T. T. Norton
    Department of Vision Sciences, Univ. of Alabama at Birmingham, Birmingham, Alabama
  • J. T. Siegwart, Jr.
    Department of Vision Sciences, Univ. of Alabama at Birmingham, Birmingham, Alabama
  • Footnotes
    Commercial Relationships T.T. Norton, None; J.T. Siegwart, None.
  • Footnotes
    Support NIH EY05922, EY03039 (CORE)
Investigative Ophthalmology & Visual Science May 2007, Vol.48, 1531. doi:https://doi.org/
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      T. T. Norton, J. T. Siegwart, Jr.; Similarities Between Myopia Induced in Tree Shrews With Form Deprivation, Minus Lenses, and Darkness. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1531. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose:: We recently found that continuous darkness produces axial elongation and myopia in visually experienced tree shrews (IOVS 47:4700, 2006). As is the case with myopia induced with form deprivation or minus lenses, dark-induced myopia is due to vitreous chamber elongation with no change in corneal curvature. We asked whether dark-induced myopia also involves an increase in the biomechanical property, "creep rate" in the sclera, and whether the myopia can be blocked by brief daily periods of light.

Methods:: Creep rate experiments: Starting at 24 days of normal visual experience (VE), tree shrews were treated with continuous darkness for 4 days (n=2) or 11 days (n=4) after which scleral creep rate was measured using 30 min periods with tensions of 1, 3 and then 5 grams. Interrupted dark experiments: Three groups of tree shrews were treated with darkness for 11 days that was interrupted daily with light for 15 minutes (n=5), 1 hr. (n=4), or 2 hrs (n=1). These were compared with a group of tree shrews (n=5) treated with continuous darkness for 11 days (reported previously).

Results:: Creep rate experiments: Continuous darkness for 4 or 11 days produced an increase in scleral creep rate (41% and 54% @ 3 gm tension) above untreated, age-matched normal animals. Increases have been found after the same durations of form deprivation (70% and 159%) and minus lens treatment (95% and 48%) (Vision Res, 39:387, 1999). Interrupted dark experiments: Continuous darkness produced a (mean ± SEM) myopic shift of -4.3 ± 0.5 D. 15 minutes of light per day did not block dark-induced myopia in 2 animals, partially blocked it in 2 animals, and completely blocked it in 1 animal (group refractive shift = -3.0 ± 0.9 D). 1 hr. of light per day produced partial blocking in all 4 animals (group refractive shift = -2.2 ± 0.8 D). 2 hrs of light per day mostly blocked myopia development in the one animal tested (refractive shift = -1.6 D). This pattern is similar to that found using short intervals of unrestricted vision to block deprivation- and lens-induced myopia.

Conclusions:: In tree shrews, dark-induced myopia shows key similarities to form deprivation and hyperopic defocus-induced myopia. Understanding how three very different visual stimuli (no light, diffuse light, and hyperopic defocus) all have a similar myopiagenic effect may shed light on the retinal signals and scleral responses that control axial elongation and refractive state.

Keywords: refractive error development • sclera • myopia 
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