Choroidal thickness measurements in different ethnicities using swept source optical coherence tomography: repeatability and assessment.

Clinical relevance: Swept-source optical coherence tomography may not provide reliable measurements of choroidal thickness for pigmented subjects.Background: The repeatability of choroidal thickness measurements in young healthy adults was investigated using swept source optical coherence tomography.Methods: Choroidal thickness was measured using swept source optical coherence tomography in 98 healthy subjects (49 South Asian and 49 Caucasian) aged between 19 and 28 years old. Repeated radial scan images centred on the fovea were obtained from the right eye with 5 min between measurements. Choroidal thickness values were obtained from the built-in automated segmentation algorithm for the 9 subfields defined by the Early Treatment Diabetic Retinopathy Study. Interclass correlation coefficients and Bland-Altman methods were used to assess test-retest repeatability.Results: The mean ± standard deviation sub-foveal choroidal thickness was 316.53 ± 63.36 µm for the Caucasian group and 292.70 ± 60.13 µm for the South Asian group. Bland-Altman analysis showed smaller test-retest variability for choroidal thickness measurements in the Caucasian group (mean difference ± SD = -0.01 ± 6.59 µm) compared to the South Asian group (mean difference ± SD = -2.38 ± 12.20 µm). No relationship was found between the mean choroidal thickness and mean spherical equivalent of refractive error for both subject groups.Conclusion: Swept source optical coherence tomography is capable of obtaining choroidal thickness measurements with good repeatability. However, test-retest limits of agreement are substantially greater in South Asian subjects, suggesting that successful identification of the choroidal scleral interface may be affected by the amount of pigmentation present in the retinal and choroidal tissues.