Effects of repeated low-level red light on refractive development during childhood: a systematic review and dose-response meta-analysis up to 12 months.

Objective: This study aimed to systematically evaluate the effects of longitudinal repeated low-level red light (RLRL) intervention on refractive development in children over a period of up to 12 months. Methods: A systematic search was conducted across four electronic databases, including randomized controlled trials involving RLRL interventions for children. The data covered literature from the establishment of each database up to August 2024. Dose-response meta-analyses were performed using a random-effects model to evaluate the impact of RLRL on refractive development at 1, 3, 6, and 12 months. Design: The research is a systematic review and meta-analysis of randomized controlled trials. Data sources: Data were searched across PubMed, Embase (Ovid), Web of Science (WoS), and the Cochrane Central Register of Controlled Trials (CENTRAL) databases from their inception to 3 August 2024. Eligibility criteria for selecting studies: Randomized controlled trials comparing RLRL with other pharmacological interventions or no treatment for refractive development in children were included. Independent data extraction was conducted, and study quality was assessed. A meta-analysis was carried out using random-effects models to evaluate the effects of RLRL on refractive development outcomes compared with control groups. Main outcomes: The main outcomes included anterior corneal curvature, axial length (AL), and spherical equivalent refractive error (SER). Results: In total, 12 unique RCTs were included. For corneal curvature, evidence for interventions with RLRL treatment being flatter than comparators was lacking (SMD = -0.01, 95%CI -0.19 to -0.12; I 2 = 0, p = 0.76). RLRL treatment was superior to comparators for both AL (SMD = 0.27, 0.06, 0.14, 0.19, 95%CI 0.20-0.33, 0.05-0.08, 0.11-0.17, 0.16-0.23; I 2 = 91, 75, 85, 85%, p < 0.01, respectively) and SER (SMD = 0.62, 0.03, 0.18, 0.32, 95%CI 0.46-0.77, -0.03 to 0.08, 0.12-0.24, 0.24-0.40; I 2 = 91, 75, 85, 85%, p = 0.05 for the 6th month and <0.01 for the remainder) in slowing the progression of myopia during 1, 3, 6, and 12 months. According to the dose-response meta-analysis, the effects of RLRL on AL and SER began to decline after 3 months of treatment. Conclusion: RLRL treatment exhibited a non-linear trend, suppressing axial length development and mitigating spherical equivalent refraction severity, with intervention efficacy diminishing by the third month, and the evidence regarding its effectiveness in flattening anterior corneal curvature remains inconclusive. Systematic review registration: https://www.crd.york.ac.uk/PROSPERO/, Identifier: CRD42024575823.