To compare the repeatability and agreement of macular thickness measurements using time domain (TD) optical coherence tomography (OCT) and spectral domain (SD) OCT in normal subjects.

Thirty-four normal subjects were included. Three consecutive macular measurements were taken with TD OCT and SD OCT. Total and regional macular thickness and total macular volume obtained by the two OCTs were compared. Within-subject standard deviation (Sw), coefficient of variation (CVw), and the intraclass correlation coefficient (ICC) were calculated to evaluate repeatability. The agreement was examined with Bland Altman plots. The correlation was also evaluated with Pearson correlation coefficients and multiple regression analysis.

Sw for foveal thickness, total macular thickness, and total macular volume were 11.53 µm, 7.58 µm, and 0.48 mm³ for TD OCT and 6.69 µm, 2.55 µm, and 0.09 mm³ for SD OCT, respectively. The values for SD OCT were consistently lower, and this result was statistically significant. The range of the respective CVw and ICC values were 1.10~2.78% and 0.78~0.96% for TD OCT, and 0.29~0.94% and 0.92~0.99% for SD OCT, respectively. The SD OCT showed better repeatability for macular thickness measurements(all with p ≤0.001). The spans of 95% limits of agreement for foveal thickness, total macular thickness, and total macular volume were 67.94 µm, 29.01 µm, and 0.98 mm³, respectively. The Pearson correlation coefficient of foveal thickness, total macular thickness, and total macular volume between the two OCT's was statistically significant.

Although both OCTs are reliable for macular thickness measurements, SD OCT shows better repeatability compared with TD OCT. Although macular thickness measurements obtained from the two OCTs can not be used interchangeably due to low agreement by different standards of measurement, there was a statistically significant correlation between the two OCT's.