Impact of 0.01% Atropine on Choroidal Thickness and Myopia Progression in Pre-Myopic Children: Insights from the AMPP Study

Purpose To investigate the effect of nightly 0.01% atropine eye drops on choroidal thickness (ChT) in pre-myopic children (at risk of myopia). Methods A 12-month randomized, double-blind, placebo-controlled trial was conducted in 54 pre-myopic children (5–12 years old). Participants received nightly 0.01% atropine or placebo in both eyes. ChT was measured in 15 macular sectors using optical coherence tomography (OCT) at baseline and every 3 months. Longitudinal mixed-effects models compared ChT changes between groups, and an unsupervised clustering analysis of individual ChT trajectories was performed. Results At 12 months, atropine-treated eyes had significantly less choroidal thinning than placebo, especially in the central, inferior, and temporal macular areas. Both groups exhibited progressive ChT thinning over time, but between-group differences became evident by 6–9 months. Clustering of ChT trajectories revealed two phenotypes: a “Thinning-dominant” pattern with pronounced mid-year thinning (6–9 months) followed by partial recovery by month 12, and a “Stable ChT” pattern with minimal change. Eyes in the Thinning-dominant group had faster axial elongation than the Stable group, suggesting that greater choroidal thinning is associated with accelerated ocular growth. Conclusions Nightly low-dose atropine in pre-myopic children slowed but did not prevent choroidal thinning, and revealed two distinct ChT response phenotypes. Greater choroidal thinning was linked to faster eye growth, indicating a structure–function relationship. ChT may serve as an early treatment biomarker, supporting timely intervention in the pre-myopia stage.