Background: Early in life, at ages corresponding to the rapid infantile phase of ocular growth in humans, visual feedback can modulate refractive development in monkeys and many other species. To determine if vision-dependent mechanisms can still influence refractive development in primates during the slow juvenile phase of ocular growth, the time period when myopia typically develops in human children, we examined the effects of form deprivation on adolescent monkeys.
Methods: Unilateral, form deprivation was produced in four rhesus monkeys by surgically fusing the eyelids of one eye. The onset of deprivation was between 3.7 and 5 years of age, which corresponds to onset ages between approximately 15 and 20 human years. The ocular effects of form deprivation were assessed by cycloplegic retinoscopy and A-scan ultrasonography.
Results: At the onset of form deprivation all four monkeys were isometropic and the axial dimensions in the two eyes were well matched. After 71 to 80 weeks of form deprivation, all of the deprived eyes had become relatively more myopic than their fellow non-treated eyes (mean anisometropia = -2.03 +/- 0.78 D) and they exhibited relative increases in vitreous chamber depth (mean = 0.55 +/- 0.31 mm) and axial length (mean = 0.49 +/- 0.35 mm).
Discussion: Our results demonstrate that vision-dependent mechanisms can influence ocular growth and refractive development in "teenage" monkeys. These results raise the possibility that visual experience may be involved in the genesis of school-age myopia in children.