Modulation of the mechanical properties of the tree shrew sclera by the visual environment

There is substantial experimental evidence that a visually guided emmetropization mechanism exists. Previous studies in tree shrews suggest that, in mammals, regulation of the mechanical properties of the sclera may be an important part of this mechanism.;To learn whether the time dependent (creep) and/or elastic properties of the sclera are regulated by the visual environment, mechanical tests were performed on 3mm wide strips of tree shrew sclera from the posterior pole. Creep rate was measured under 1, 3, and 5 grams of uniaxial tension (30 minutes at each level). The modulus of elasticity was calculated from the elastic extensions that occurred when the force was increased at the beginning of each of the three phases. Stiffness values were obtained from a load displacement test.;Five experimental conditions were examined: (a) normal development; (b) monocular form deprivation (MD), which increases axial elongation rate; (c) recovery from MD, which decreases axial elongation rate; (d) monocular ;Creep rate was similar in the right and left eyes of normally developing animals. Four days of MD produced a 200 to 300% increase in creep rate in the deprived eyes that remained similarly high after 11 and 21 days of MD. After 10 days of recovery, following 11 days of MD, the creep rate in the recovering eyes returned to normal levels. In animals that wore a ;These data show that the time dependent (creep) properties of the sclera are regulated by the visual environment, while the elastic properties, at near physiological stress levels are not. The temporal correspondence between changes in axial elongation rate and creep rate suggest that regulation of scleral mechanical properties may play a role in controlling axial elongation rate.