Nonlinear effect of light intensity on normal axial development of rhesus monkeys

Purpose To investigate the effects of different indoor lighting intensity (500 lx, 750 lx and 1,000 lx) on normal ocular axial length growth by using juvenal rhesus monkeys. Methods Twenty-four juvenile monkeys were exposed continuously to normal intensity light (NIL, 500 lx, n=16), medium intensity light (MIL, 750 lx, n=8) and high intensity light (HIL, 1 000 lx, n=8), with a same CCT value (about 3000 K) for 246 days. Axial length, anterior chamber depth, corneal curvature radius were measured at about a monthly interval. Results After 246 days of light exposure, the growth of axial length of the MIL group (750 lx) were 0.151 ± 0.081 mm and 0.139 ± 0.070 mm in the right and left eyes, respectively, and significantly larger in comparison with the NIL group (500lx, OD: 0.068 ± 0.055 mm, OS: 0.074 ± 0.057 mm) and the HIL group (1000lx,OD:0.063 ± 0.093 mm, OS: 0.084 ± 0.052 mm) monkeys. This effect was stable and robust during the whole experimental period. Conclusion The effects of different intensity lighting on normal ocular axial development was not linear as most people currently think. We must be cautious when it comes to elevate light intensity in classrooms. Whether this conclusion is correct under lights of other CCT value needs further study. ### Competing Interest Statement The authors have declared no competing interest.