The effect and safety of violet light exposure for suppression of lens-induced myopia in guinea pigs.

PURPOSE: To determine safe and effective parameters for violet light (VL, 360-400 nm) exposure in suppressing myopia progression and to identify retinal signaling pathways responsive to VL irradiation.

METHODS

Three-week-old guinea pigs underwent monocular -10D lens-induced myopia (LIM) for 4 weeks and were randomized to white-light alone or white-light plus VL exposure varying in irradiance (40, 100, 400 μW/cm2 for 3 h/day) or exposure duration (40 μW/cm2 for 1, 3, 6, or 12 h/day). Refractive error, axial length (AL), vitreous chamber depth (VCD), retinal thickness (RT), choroidal thickness (ChT), choroidal blood perfusion (ChBP), and corneal fluorescein staining were measured every 2 weeks. HE staining, apoptosis, and retinal dopamine transporter (DAT), phosphorylated dopamine transporter were assessed.

RESULTS

When the irradiation protocol was 40 μW/cm2 for 3 h/day, VL had the maximum inhibitory effect on myopia, attenuating the myopic shift (-6.341 ± 0.190 D vs -1.332 ± 0.223 D) and axial length elongation (7.690 ± 0.016 mm vs 8.008 ± 0.011 mm). The inhibitory effects of high VL irradiation intensity and long VL irradiation time on LIM are both weakened. The changes in ChT and ChBP induced by LIM were reduced by VL irradiation. High irradiation dose of VL resulted in slight corneal epithelial and retinal damage. After VL irradiation, the phosphorylation level of DAT was up-regulated.

CONCLUSIONS

VL exposure significantly reduced myopia shift and axial elongation with the most effective dose at 40 μW/cm2, 3 h/day, beyond which efficacy declines and ocular safety is reduced. VL light increases the level of DAT phosphorylation, which may be an intrinsic mechanism by which VL controls myopia.