Abstract
Purpose: :
To determine whether high ambient lighting levels retard the development of vision-induced myopia in infant monkeys.
Methods: :
Monocular form deprivation was optically imposed on 24 rhesus monkeys using diffuser spectacles. Throughout the diffuser rearing period, which extended from 3 weeks of age until at least 100 days of age, 18 of the treated monkeys were exposed to normal laboratory lighting levels (up to 630 lux) on a 12-hr light - 12-hr dark cycle. For the other 8 form-deprived monkeys, an auxiliary lighting system increased the cage level illuminance to 18,000 to 28,000 lux for 6 hours during the middle of the daily 12-hr light cycle. Refractive development was assessed periodically by retinoscopy and A-scan ultrasonography. Control data were obtained from 32 normal monkeys.
Results: :
Form deprivation produced relative axial myopia in the treated eyes of 14 of the 18 monkeys reared under normal lighting levels. In contrast, by 95 days of age only 1 of the 8 form-deprived monkeys reared under the high-light conditions developed a significant myopic anisometropia and in 6 of the 8 high-light-reared monkeys, the form-deprived eyes were more hyperopic than the control eyes. In comparison to normal monkeys, the median refractive errors for the treated eyes of the high-light-reared monkeys were more hyperopic (+4.97 vs +2.53 D; P = 0.02). As a consequence, the high-light-reared monkeys exhibited significantly lower average degrees of myopic anisometropia (+0.14 ± 4.12 vs -3.56 ± 3.33 D, P = 0.04) and the average treated-eye refractive errors were significantly more hyperopic than those observed in the form-deprived monkeys reared under normal light levels (+4.44 ± 5.24 vs -0.65 ± 3.84 D, P = 0.03).
Conclusions: :
High ambient light levels can dramatically retard the development of form-deprivation myopia in infant monkeys. These results show that absolute light levels are a fundamental variable impacting the vision-dependent regulation of ocular growth in primates and suggest that the protective effects of outdoor activities against myopia in children are due to exposure to the higher light levels normally encountered in outdoor environments.
Keywords: myopia • emmetropization • refractive error development