Effects on choroid after repeated low-level red-light therapy in preclinical and clinical myopic children: a randomized controlled trial

PURPOSE: To evaluate how choroidal thickness (CT) and choriocapillaris flow deficit density (CCD) change within 6000 µm of the macula following repeated low-level red-light (RLRL) therapy, and to assess whether early choroidal alterations can predict long-term myopia control. METHODS: This is a secondary analysis of a prospective randomized controlled trial. Two hundred children with spherical equivalent refraction (SER) of -6.00D to +0.50D were randomized to receive either twice-daily RLRL therapy or no additional intervention (control). Axial length (AL), cycloplegic SER, CT, and CCD were measured at the baseline and at 1, 3, 6 and 12 months. RESULTS: Baseline characteristics were similar between groups. In the RLRL group, subfoveal choroidal thickness (SFCT) increased progressively over time, reaching its maximum at 12 months; by contrast, SFCT declined in controls. Within the 6000 µm macular zone, CT rose in the RLRL group but fell uniformly in the control group. Improvements on choriocapillaris blood flow were evident at 3 months post-RLRL, yet these changes were not sustained and did not correlate with longer-term choroidal thickening. A prediction model using only the "6-month SFCT change" demonstrated comparable accuracy for forecasting satisfactory myopia control at 12 months to more complex multivariable models. CONCLUSIONS: RLRL therapy induces a marked and sustained thickening of the macular choroid within 6000 µm, while its effects on choriocapillaris perfusion are transient. Moreover, the magnitude of SFCT increase at 6 months alone provides a reliable early predictor of 12-month myopia control efficacy. Trial Registration This trial was registered at the Chinese Clinical Trial Registry on January 30, 2021, with trial registration number: ChiCTR2100042836. https://www.chictr.org.cn/showprojEN.html?proj=120971.