Abstract
Purpose: :
In infant monkeys, high levels of artificial lighting can dramatically reduce the degree of axial myopia produced by form deprivation. The aim of this investigation was to determine whether high light levels would retard the development of negative-lens-induced myopia in primates.
Methods: :
Hyperopic defocus was monocularly imposed on 18 infant monkeys by securing -3 D lenses in front of the treated eyes and zero-powered lenses in front of the fellow eyes. The lens-rearing procedures were initiated at 25 ± 3 days of age; the animals wore the lenses continuously for periods of at least 84 days. Throughout the treatment period 10 of the lens-reared monkeys were exposed to normal laboratory lighting (up to 630 lux) on a 12-hour-light / 12-hour-dark cycle. For the other 8 lens-reared monkeys, an auxiliary lighting system increased the cage level illuminance to about 25,000 lux for 6 hours during the middle of the daily light cycle. Refractive development and the eye’s axial dimensions were assessed by retinoscopy and A-scan ultrasonography, respectively. Control data were obtained from 32 normal monkeys.
Results: :
After 84 days of lens wear, 8 of the 10 treated monkeys reared under normal lighting levels and 7 of the 8 monkeys reared under high ambient lighting had developed compensating axial myopic anisometropias that were outside 2 standard deviations of the mean for normal monkeys. However, there were no differences in the median anisometropias between the high-light-reared (-2.49 D) and normal-light-reared monkeys (-1.88 D, P=0.56). There was a trend for myopic changes to develop slower in the high-light-reared animals. For example, after 21 days of lens wear the median anisometropias for the high- and normal-light-reared monkeys were -0.67 and -1.23 D, respectively. However, these differences did not reach statistical significance (P=0.07).
Conclusions: :
High ambient lighting does not obviously alter the time course or the end point for compensation to negative lenses in infant monkeys. As previously observed in chickens, high light levels appear to have a greater protective effect on form-deprivation myopia than on negative-lens-induced myopia, most likely reflecting qualitative differences in the underlying processes for these two common forms of vision-induced myopia.
Keywords: refractive error development • myopia • hyperopia