THE SUSCEPTIBLE PERIOD FOR DEPRIVATION-INDUCED MYOPIA IN TREE SHREW

To examine the susceptible period for deprivation-induced myopia, six groups of tree shrew pups (Tupala glis belangeri) were monocularly dep rived for 12 days with an opaque occluder starting 7, 15, 21, 33, 48, or 63 days after natural eyelid opening. Compared to the untreated fel low control eye, significant myopia and vitreous chamber elongation we re produced by the deprivation in all six groups. The effect was great er in the middle three groups in comparison with the youngest and the two oldest groups and the amount of induced myopia and axial elongatio n was not proportional to the normal rate of axial growth. The peak pe riod of susceptibility was between approximately 15 and 45 days after eye opening during the juvenile, slow-elongation phase of ocular devel opment when the eye is within 7% of its adult axial length. Significan t myopia and axial elongation were also induced in adult animals by 70 days of monocular deprivation. To examine recovery from deprivation-i nduced myopia, the occluder was removed at the end of the 12 day depri vation period. After an additional 48 days of binocular visual experie nce, no significant myopia was present in the previously deprived eyes in any experimental group. During the recovery period, the elongation rate of the previously deprived eyes was reduced in comparison with t he control eyes while normal corneal flattening and lens development c ontinued, thus reducing the myopia. No difference in corneal curvature , relative to the untreated control eyes, was found after deprivation or after the recovery period. Data are presented which suggests that c hanges in the thickness of the choroid may occur in this mammal during deprivation and recovery that are in the same direction, but of small er magnitude, than those reported in the chicken. The results of this study provide evidence that visually guided emmetropization occurs in this mammalian species during a period of ocular development analogous to the juvenile period in humans. (C) 1998 Elsevier Science Ltd. All rights reserved.