Short-Term Effects of Low-Level Red-Light Therapy on Central Retinal Function: A Combined Pattern ERG and Photopic ERG Study

Background: Low-level red-light therapy (RLRT) has emerged as a potential therapy in myopia management. However, its effects on retinal structure and function following repeated exposure remain incompletely understood. Purpose: To evaluate the short-term effects of RLRT on central retinal function in myopes and non-myopes using retinal electrophysiology and structural parameters. Methods: Thirty-six subjects underwent RLRT exposures. Retinal function was assessed using pattern electroretinography (PERG) and photopic full-field electroretinography (Photopic 3.0 ERG). Structural measurements, including axial length (AL), obtained with an optical biometer and choroidal thickness (CT), were measured using MOPTIM 3000. Outcomes were compared between baseline and post-RLRT conditions (single 3 min and single 1 min exposure), across refractive groups, and correlated with AL and CT. This study was conducted at the University of Minho in accordance with the Declaration of Helsinki. Results: In myopic subjects, PERG N35-P50 amplitude significantly increased after 3 min of RLRT (baseline:0.88 ± 0.21 µV; post: 1.40 ± 0.25 µV; p = 0.013), whereas no significant changes were observed in non-myopes (baseline: 1.32 ± 0.19 µV; post: 1.39 ± 0.21 µV; p = 0.47). Latencies remained stable across all groups (p > 0.05). No significant correlations were found between PERG and AL (ρ = -0.18, p = 0.44) or CT (ρ = 0.12, p = 0.52). Photopic 3.0 ERG showed an increase in b-wave amplitude after 3 min of RLRT in myopes (Δ = +2.42 µV, p = 0.06), but not in non-myopes. In myopes, AL was negatively correlated with post-therapy latency (ρ = -0.624, p = 0.060), while CT showed strong correlations with photopic a-wave responses after 1 min RLRT (CT vs. latency: ρ = -0.873, p = 0.010; CT vs. amplitude: ρ = 0.821, p = 0.034). Conclusions: Short-term exposure to RLRT, particularly at 3 min, enhances PERG and Photopic ERG responses in myopic subjects, suggesting transient improvements in retinal function with differential effects between refractive groups.