Acute Ocular Effects of Violet and Red Light Exposure in Young Adults.

PURPOSE: To evaluate short-term effects of violet, red and combined violet and red light exposure on axial length, choroidal thickness and vascular perfusion in adults as a step toward understanding acute ocular responses to spectral illumination. METHODS: Twenty participants (ages 28.2 ± 3.5 years) completed four sessions on separate days of 60 min exposure to either (1) broadband, (2) violet (peak 400 nm), (3) red (peak 628 nm) or (4) combined violet + red light. Biometry (LenStar) and optical coherence tomography and angiography (Spectralis) were performed at baseline, after exposure and after 30 min of recovery. Axial length, choroidal thickness, perfusion density of the superficial and deep vascular complex and choriocapillaris and foveal vascular zone were analysed across time and light conditions. RESULTS: Choroidal thickness decreased significantly over time across lighting conditions (p < 0.001) while no significant main effect of condition (p = 0.27) or condition-by-time interaction (p = 0.44) was observed. Bonferroni-adjusted within-condition comparisons showed significant reductions in choroidal thickness following 60 min of violet (-4 ± 1 µm) and red light exposure (-8 ± 2 µm) relative to baseline (all p ≤ 0.02). No significant changes were observed under broadband or combined violet + red light. Axial length and vascular metrics did not change significantly with time or lighting condition (all p > 0.21). CONCLUSION: Short-term exposure to narrowband red and violet light was associated with modest reductions in choroidal thickness in young adults; however, changes did not differ significantly across lighting conditions. Combined red and violet light exposure produced no measurable effect. Together, these findings suggest that acute ocular responses to spectral illumination are limited under the conditions tested and do not support distinct wavelength-specific effects in young adults.