Protective effects of high ambient lighting on the development of form-deprivation myopia in rhesus monkeys

Abstract

Purpose: Time spent outdoors reduces the likelihood that children will develop myopia, possibly because light levels are much higher outdoors than indoors. To test this hypothesis, the effects of high ambient lighting on vision-induced myopia in monkeys were determined.

Methods: Monocular form deprivation was imposed on eight infant rhesus monkeys. Throughout the rearing period (23 ± 2 to 132 ± 8 days), auxiliary lighting increased the cage-level illuminance from normal lighting levels (15-630 lux) to ∼25,000 lux for 6 hours during the middle of the daily 12-hour light cycle. Refractive development and axial dimensions were assessed by retinoscopy and ultrasonography, respectively. Comparison data were obtained in previous studies from 18 monocularly form-deprived and 32 normal monkeys reared under ordinary laboratory lighting.

Results: Form deprivation produced axial myopia in 16 of 18 normal-light-reared monkeys. In contrast, only 2 of the 8 high-light-reared monkeys developed myopic anisometropias, and in 6 of these monkeys, the form-deprived eyes were more hyperopic than their fellow eyes. The treated eyes of the high-light-reared monkeys were more hyperopic than the form-deprived eyes of the normal-light-reared monkeys. In addition, both eyes of the high-light-reared monkeys were more hyperopic than those of normal monkeys.

Conclusions: High ambient lighting retards the development of form-deprivation myopia in monkeys. These results are in agreement with the hypothesis that the protective effects of outdoor activities against myopia in children are due to exposure to the higher light levels encountered outdoors. It is possible that therapeutic protection against myopia can be achieved by manipulating indoor lighting levels.

Figure 1.

Spherical-equivalent refractive corrections (A–E) and vitreous chamber depths (F–J) plotted as a function of age for the treated and fellow eyes of five representative form-deprived monkeys that were reared under ordinary laboratory lighting. Thin lines: the data for the right eyes of the control monkeys. The first symbols in each plot represent the onset of the diffuser rearing period. The diffusers were worn continuously throughout the observation period.

Figure 2.

Spherical-equivalent refractive corrections plotted as a function of age for the treated and fellow eyes of the eight form-deprived monkeys (A–H) that were reared under high ambient lighting conditions. Thin lines: the data for the right eyes of the control monkeys. The first symbols in each plot represent the onset of the diffuser rearing period; the diffusers were worn continuously throughout the observation period.

Figure 3.

Interocular differences in spherical-equivalent refractive error (treated eye refractive correction − fellow eye refractive correction) plotted as a function of age for individual form-deprived monkeys. The first and last symbols for each animal correspond to the start and the end of the treatment period, respectively. Data are shown from the monocularly form-deprived monkeys reared under (A) normal laboratory lighting or under (B) high levels of artificial lighting.

Figure 4.

Spherical-equivalent refractive errors obtained at ages corresponding to the end of the treatment period for both eyes of individual monkeys. (◊) Normal monkeys and the fellow eyes of the form-deprived monkeys; (◆) the treated eyes of the form-deprived monkeys reared under the normal and high ambient light levels.

Figure 5.

Vitreous chamber depth plotted as a function of age for the treated and fellow eyes of individual form-deprived monkeys that were reared under high artificial lighting (A–H). Thin lines: data for the right eyes of the control monkeys. The first symbols in each plot represent the onset of the diffuser rearing period.

Figure 6.

Interocular differences in refractive error plotted as a function of interocular differences in vitreous chamber depth for individual animals (treated or right eye − fellow or left eye). Solid line: best-fitting regression line (y = −5.71x − 0.10; r² = 0.91).