BackgroundDespite receiving orthokeratology (ortho-k), the efficacy of retarding ocular elongation during myopia varies among myopic children. The current study aimed to investigate the early changes of choroidal vasculature at one month after ortho-k treatment and its association with one-year ocular elongation, as well as the role of such choroidal responses in predicting the one-year control efficacy of ortho-k treatment.MethodsA prospective cohort study was conducted in myopic children treated with ortho-k. Myopic children aged between 8 and 12 years who were willing to wear ortho-k lenses were recruited consecutively from the Eye Hospital of Wenzhou Medical University. Subfoveal choroidal thickness (SFCT), submacular total choroidal luminal area (LA), stromal area (SA), choroidal vascularity index (CVI), choriocapillaris flow deficit (CcFD) were evaluated by optical coherence tomography (OCT) and OCT angiography over a one-year period.ResultsFifty eyes from 50 participants (24 males) who finished one-year follow-ups as scheduled were included, with a mean age of 10.31 ± 1.45 years. The one-year ocular elongation was 0.19 ± 0.17 mm. The LA (0.03 ± 0.07 mm2), SA (0.02 ± 0.05 mm2) increased proportionally after one-month of ortho-k wear (bothP< 0.01), as did the SFCT (10.62 ± 19.98 μm,P< 0.001). Multivariable linear regression analyses showed that baseline CVI (β = − 0.023 mm/1%, 95% CI: − 0.036 to − 0.010), one-month LA change (β = − 0.009 mm/0.01 mm2, 95% CI: − 0.014 to − 0.003), one-month SFCT change (β = − 0.035 mm/10 µm, 95% CI: − 0.053 to − 0.017) were independently associated with one-year ocular elongation during ortho-k treatment after adjusting with age and sex (allP< 0.01). The area under the receiver operating characteristic curve of prediction model including baseline CVI, one-month SFCT change, age, and sex achieved 0.872 (95% CI: 0.771 to 0.973) for discriminating children with slow or fast ocular elongation.ConclusionsChoroidal vasculature is associated with ocular elongation during ortho-k treatment. Ortho-k treatment induces increases in choroidal vascularity and choroidal thickness as early as one month. Such early changes can act as predictive biomarkers of myopia control efficacy over a long term. The utilization of these biomarkers may help clinicians identify children who can benefit from ortho-k treatment, and thus has critical implications for the management strategies towards myopia control.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40662-023-00345-2.