Effects of Orthokeratology on Choroidal Thickness and Axial Length

Purpose To investigate the effect of orthokeratology (ortho-k) treatment on choroidal thickness and its relationship with axial length change. Methods Seventy-seven myopic subjects aged between 7 and 17 years were treated with ortho-k lenses (n = 39) or single-vision spectacle lenses (SVL, n = 38). Choroidal thickness and axial length measurements were taken at baseline and repeated 1 week and 3 weeks after lens wear for the ortho-k group and at 3 weeks for the SVL group. Parafoveal choroidal thickness was assessed using optical coherence tomography and segmented into nine regions according to the Early Treatment Diabetic Retinopathy Study (ETDRS) within a 6 x 6 mm circular zone centered on the fovea. Axial length was measured using partial coherence interferometry. The changes in subfoveal choroidal thickness were compared to the changes in axial length in both study groups. Results The change in axial length was significantly correlated with the change in choroidal thickness in both groups at 3 weeks (ortho-k, r = -0.351, p = 0.028 vs. SVL, r = -0.408, p = 0.011). Parafoveal choroidal thickness increased after 3 weeks of lens wear in the ortho-k group (mean, 21.8 25.2 m) but did not change in the SVL group (mean, 0.1 +/- 19.7 m). Choroidal thickness significantly varied across the posterior retinal regions (F = 82.14, p < 0.001), with the temporal regions being thickest and nasal regions being thinnest. After 3 weeks of ortho-k treatment, the magnitude of change (range, 14.1-27.6 m) in choroidal thickness of the nine ETDRS regions was proportional to the baseline choroidal thickness in those regions (r = 0.88, p = 0.002). Axial length did not significantly change over time (F = 0.001, p = 0.975) and did not differ between the two treatment modalities (F = 0.305, p = 0.582). Conclusions Choroidal thickness increases after short-term ortho-k treatment. Regional choroidal thickening after ortho-k treatment may be attributable to the altered retinal defocus profile associated with ortho-k lens wear.