Mapping Regional Choroidal Thickness Changes During Myopia Control in Children: A 24-Month Secondary Analysis of the ASPECT Randomized Trial

Background/Objectives: Choroidal thickness (ChT) changes have been proposed as biomarkers of myopia-control response, but their regional pattern and relationship with axial elongation remain uncertain. We evaluated regional choroidal responses to adding. Defocus Incorporated Multiple Segments (DIMS) spectacles to 0.025% atropine, and asessed biomarker potential of regional and baseline ChT. Methods: This secondary analysis included ASPECT participants with enhanced-depth imaging OCT scans. In ASPECT, 111 myopic children aged 4–16 years were randomized to nightly 0.025% atropine plus DIMS or single-vision spectacles. ChT was measured subfoveally and 1000 µm nasally and temporally at baseline and 6, 12, 18, and 24 months using a validated automated segmentation pipeline. Linear mixed-effects models assessed longitudinal and between-group differences, associations with axial elongation, and effect modification by baseline ChT. Results: 101 children completed 24 months (53 atropine plus DIMS; 48 atropine plus single-vision). In the DIMS group, mean 24-month ChT increases were largest temporally (+22.2 µm), followed by nasally (+15.5 µm) and subfoveally (+10.6 µm). Between-group differences favored DIMS, significant temporally at all visits (p = 0.009–0.040) and nasally at 6, 12, and 24 months (p = 0.030–0.040); no significant subfoveal differences were found. Regional ChT changes were not significantly associated with axial elongation, and baseline ChT did not modify the treatment effect. Conclusions: Over 24 months, ChT showed a region-specific treatment response, most consistent temporally, less consistent nasally, and subfoveally. Regional ChT may offer an exploratory marker of treatment-related remodelling, but its predictive value for individualised treatment remains uncertain.