Clinically Significant Axial Shortening in Myopic Children After Repeated Low-Level Red Light Therapy: A Retrospective Multicenter Analysis

Introduction: Myopia is recognized as a progressive eye disease. The aim of this study was to evaluate the frequency and associated factors of clinically significant axial length (AL) shortening among myopic children following repeated low-level red light (RLRL) therapy.Methods: The clinical data that were collected for the myopic children aged 3-17 years who received an RLRL therapy delivered by home-use desktop light device that emitted light at 650 nm for at least 1 year, were reviewed. The clinical data included AL, spherical equivalent refraction (SER), and visual acuity measured at baseline and follow-up. The primary outcomes were frequency of AL shortening of > 0.05 mm, > 0.10 mm, and > 0.20 mm per year, and associated factors of AL shortening per year.Results: A total of 434 myopic children with at least 12 months of follow-up data were included. The mean age of participants was 9.7 (2.6) years with SER of -3.74 (2.60) diopters. There were 115 (26.50%), 76 (17.51%), and 20 (4.61%) children with AL shortening based on cutoffs of 0.05 mm/year, 0.10 mm/year, and 0.20 mm/year, respectively. In the multivariable model, AL shortening was significantly associated with older baseline age, female gender, and longer baseline AL or greater spherical equivalent refraction (all P < 0.05). Among AL shortened eyes, the mean AL difference (standard deviation, SD) was -0.142 (0.094) mm/year. Greater AL shortening was observed among children who were younger and had longer baseline AL (all P < 0.05).Conclusions: More than a quarter of children had AL shortening > 0.05 mm following RLRL therapy, and the overall mean AL change was -0.142 mm/year. Further studies should explore the mechanisms underlying AL shortening.