Morphology of tree shrew sclera and choroid during normal development, induced myopia, and recovery

Academic Article

Abstract

  • Purpose. To examine changes in sclera and that may underlie the control of axial elongation during emmetropization, a light microscopic examination was made of eyes from normal developing tree shrews, eyes with form-deprivation induced myopia, and eyes recovering from an induced myopia. Methods. Scleral location, choroidal thickness and scleral thickness were measured in 2.5 μm horizontal Spurr-embedded sections of the eyes from animals that had 1, 15, 45, 75, and 110 days of normal visual experience (v.e.)[N=4 per group], from monocularly deprived (MD) animals (from 24 to 45 days v.e.; N=4), and from animals that recovered for 30 days (45-75 days v.e.) following 21 days of MD (N=4). Results. During normal development, the sclera moved posteriorly as the vitreous chamber enlarged. The change was rapid before 15 days of v.e. and slower during the juvenile period. The sclera of eyes with an induced myopia was displaced posteriorly in comparison to fellow control eyes. After 30 days of recovery, the sclera was no longer significantly displaced vs. controls. Choroidal thickness and choroidal cross-sectional area (an index of volume) were smaller than in control eyes after deprivation and larger after recovery. Only the deprived vs. recovery measures differed significantly. The sclera gradually increased in thickness during development, especially in the region of attachment of the extraocular muscles. In myopic vs. control eyes, the sclera was thinner posteriorly and smaller in cross-sectional area. These values increased only slightly after recovery. A small, not-significant thinning of the control eye sclera was noted. Conclusions. Both the choroid and sclera appear to thin in eyes with a deprivation-induced myopia, in excess of the amount needed to cover the enlarged globe. The choroid changes can have only small optical effects (∼1 D). These results are consistent with biochemical and biomechanical studies showing reduction of scleral extracellular matrix and increased scleral creep in eyes with induced myopia.
  • Authors

    Author List

  • Norton TT; Kang RN
  • Volume

  • 37
  • Issue

  • 3