Repeatability and Agreement of Macular Thickness Measurement Using Time and Spectral Domain OCT in Diabetic Macular Edema

ABSTRACT

PURPOSE: To evaluate the repeatability of macular thickness measurements using time domain (TD) OCT and spectral domain (SD) OCT in diabetic macular edema. METHODS: In 42 eyes of 42 patients with diabetic macular edema, three consecutive macular measurements were performed with TD OCT and SD OCT, and measurements for macular thickness and total macular volume obtained by the two OCTs were compared. The within-subject standard deviation (Sw), coefficient of variation (CVw), and intraclass correlation coefficient (ICC) were calculated to assess repeatability, with agreement between measurements assessed with Bland Altman plots. The correlations were also evaluated via the Pearson's correlation coefficient. RESULTS: The Sw of TD OCT and SD OCT for foveal thickness, total macular volume were 29.67 micrometer/16.44 micrometer, 1.26 mm3/0.23 mm3, respectively, and were significantly lower in SD OCT. The ranges of the respective CVw and ICC values were 1.10-2.78%, 0.78~0.96 for TD OCT, and 0.29~0.94%, 0.92~0.99 for SD OCT. The SD OCT showed better repeatability for macular thickness measurements (all p< or =0.001). The 95% limits of agreement for foveal and total macular volume were 88.9 micrometer, 2.4 mm3, respectively. The Pearson's correlation coefficients of macular thickness and total macular volume between the two OCT methods were statistically significant (p=0.88-0.99). CONCLUSIONS: Although both OCTs proved reliable for macular thickness measurements in diabetic macular edema, SD OCT shows better repeatability than TD OCT. Although macular thickness measurements obtained from the two OCTs cannot be used interchangeably, there were statistically significant correlations between measurements obtained using the two OCTs.