AIM: To investigate choroidal thickness changes in the horizontal meridian after orthokeratology. METHODS: This is a prospective cross-sectional observed study. Subjects (n=30; 11.3±1.7y) with low-to-moderate myopia (-1.0 to -6.0 diopters), wore orthokeratology (Ortho-K) lenses for 3mo. Before and after Ortho-K, OCT scans were made through the fovea in the horizontal meridian. Choroid thickness around the fovea was acquired by custom software. The analyzed regions along the horizontal meridian were divided into 7 equal zones. Ocular parameters were measured by Lenstar LS 900 non-contact biometry. RESULTS: Only the right eye ocular parameters were analyzed in this study. Before Ortho-K, choroidal thickness along the horizontal meridian was 273.7±31.8 μm in the temporal zone, 253.1±38.6 μm in the macula zone, and 194.8±52.2 μm in the nasal zone. After Ortho-K, the choroid was thicker in each horizontal zone (P<0.05). The increased thickness was greatest in the temporal zone (13.5±22.5 μm) and least in the nasal zone (8.4±14.2 μm). The axial length (AL) increased 0.02 mm (P>0.05). The choroid thickness change in each horizontal zone was negatively correlated with AL (r, -0.3 to -0.4; P<0.05) except one of the nasal zones. CONCLUSION: In myopic children, the thickness of the choroid is greatest in the temporal zone and thinnest in the nasal zone. After nightly Ortho-K for 3mo, the thickness increase along the horizontal meridian. The choroid thickness changes are negatively correlated with the change of AL.