Contributions from light level and spectral content on refractive development in young rabbits

AIM: To compare the effects of manipulating light levels versus manipulating the spectral content of short wavelengths (blue light) of ambient lighting on refractive development in young rabbits. METHODS: A total of 32 healthy 3-week-old rabbits were randomly assigned to one of the four groups with 8 in each group for 12wk: Control group (NC) under low blue light (output ratio of blue light 1.8%) at low illuminance (341 lx), HI group under low blue light (output ratio of blue light 1.6%) at high illuminance (5057 lx), simulating natural light (S-NL) group under high blue light (output ratio of blue light 4.9%) at high illuminance (5052 lx), and MB group under high blue light (output ratio of blue light 5.2%) at low illuminance (342 lx). The lighting in each group were provided by light emitting diode (LED) lamps emitting visible light (range 380-780 nm) in addition to (or not) LED lamps only emitting short wavelength (range 380-500 nm). Refraction, axial length, and corneal curvature radius were assessed by retinoscopy, ultrasonography and keratometry, respectively. Average data of both eyes for each animal were used as single values and compared among groups. RESULTS: During the 12-week intervention, all animals had an emmetropization period. The decrease of refraction in rabbits in HI group was similar to S-NL group, both slower than that of NC group (P<0.001). At the 12th week, the refraction (3.000±0.267 D) and vitreous cavity depth (7.421±0.168 mm) of S-NL was similar to HI group (3.250±0.267 D, 7.264±0.256 mm), significantly different from NC group (1.937±0.291 D, 7.825±0.313 mm; P<0.001 for both). High blue light at low illuminance had little effect on refraction change. At the end of intervention, the difference of refraction (2.219±0.281 D) and vitreous cavity depth (7.785±0.229 mm) in MB group were not statistically significant (P=0.311, P=0.749) compared with NC group. The other components were less affected by lighting conditions (P>0.05). CONCLUSION: The light levels per se but not the rich in spectral content of short wavelengths determine the inhibitory effect of ambient lighting on myopia development in rabbits.