Comparability of retinal thickness measurements using different scanning protocols on spectral-domain optical coherence tomography.

Retinal thickness measurements obtained using optical coherence tomography (OCT) play an essential role both in multi-center clinical trials and in normal clinical practice. Different scanning protocols are available on most OCT devices, and it is important to ascertain whether the retinal thickness measurements obtained from these are comparable. This study aimed to compare retinal thickness measurements between raster and radial scanning protocols using spectral-domain OCT (SD-OCT). In a prospective study, 32 healthy subjects were scanned sequentially using raster and radial protocols from a SD-OCT device. For both the raster and radial OCT scans, retinal thicknesses were measured manually subfoveally and at 12 other points at 0.5 mm intervals temporally and nasally on the horizontal OCT B-scan passing through the fovea. The retinal thickness measurements were compared using intraclass correlation (ICC) and Bland-Altman plots. Subfoveal retinal thickness was 227.0 µm when measured on the raster scan and 229.2 µm on the radial scan, with a mean difference of 2.2 µm (P = 0.141).The ICC for agreement was 0.889 (95 % confidence interval 0.818-0.933). Similar results were observed for retinal thickness measurements at all other points, with mean differences ranging from -3.37 to 2.59 µm, and ICC values ranging from 0.837 to 0.972. The retinal thickness measurements obtained by the raster and radial scans of the same SD-OCT device are comparable, with differences of less than 4 µm. This is of relevance when measurements made using different OCT scan protocols are compared.