Choroidal thinning in high myopia measured by optical coherence tomography

PURPOSE: To investigate the rate of choroidal thinning in highly myopic eyes. PATIENTS AND METHODS: A retrospective observational study of 37 eyes of 26 subjects (nine males and 17 females, mean age 39.6 ± 7.7 years) with high myopia but no pathologies who had undergone spectral domain optical coherence tomography and repeated the test 1 year later (1 ± 0.25 year) at Osaka University Hospital, Osaka, Japan. Patients older than 50 years with visual acuity worse than 20/40 or with whitish chorioretinal atrophy involving the macula were excluded. Two masked raters measured the choroidal thicknesses (CTs) at the fovea, 3 mm superiorly, inferiorly, temporally, and nasally on the images and averaged the values. The second examination was about 365 days after the baseline examination. The CT reduction per year (CTRPY) was defined as (CT 1 year after – baseline CT)/days between the two examinations × 365. The retinal thicknesses were also investigated. RESULTS: The CTRPY at the fovea was −1.0 ± 22.0 μm (range −50.2 to 98.5) at the fovea, −6.5 ± 24.3 μm (range −65.8 to 90.2) temporally, −0.5 ± 22.3 μm (range −27.1 to 82.5) nasally, −9.7 ± 21.7 μm (range −40.1 to 60.1) superiorly, and −1.4 ± 25.5 μm (range −85.6 to 75.2) inferiorly. There were no significant differences in the CTRPY at each location (P = 0.34). The CT decreased significantly (P < 0.05) only superiorly. The superior CTRPY was negatively correlated with the axial length (P < 0.05). The retinal thickness at the fovea did not change. Stepwise analysis for CTRPY selected axial length (P = 0.04, R(2) = 0.13) and age (P = 0.08, R(2) = 0.21) as relevant factors. CONCLUSIONS: The highly myopic choroid might gradually thin and be affected by many factors. Location and axial length are key factors to regulate the rate of choroidal thinning in highly myopic eyes. Overall choroidal thickness was not found to change significantly. Longer follow-ups are needed.