Comparison of retinal nerve fiber layer measured by time domain and spectral domain optical coherence tomography in optic neuritis

Purpose To study the relationship between retinal nerve fiber layer (RNFL) thickness measurements from time domain (Stratus) and spectral domain (Cirrus HD) optical coherence tomography (OCT) in subjects with optic neuritis. Methods A total of 18 patients who had suffered monocular acute optic neuritis were imaged by a single trained operator using the Stratus-OCT (fast RNFL scan mode) and Cirrus HD-OCT (optic disc cube mode) on the same day. The relationship between RNFL thickness measurements of the two OCTs (overall and by quadrants) were evaluated using intraclass correlation coefficient (ICC) and Bland-Altman plots. Comparisons between eyes having optic neuritis (ON-group) and fellow eyes (fellow-group) were assessed by a generalized estimating equation (GEE) regression model. Results For Stratus-OCT, the median average RNFL was 86.3 and 102 mu in the ON-group and in the fellow-group, respectively. For Cirrus-OCT, the corresponding measurements were 81 and 93 mu. Average RNFL thickness as determined by the two OCT devices was well correlated in the ON-group (rho = 0.906, P < 0.001) and in the fellow-group (rho = 0.702, P = 0.001). The median signal strength was significantly higher with Cirrus-OCT. Bland-Altman plots showed that Stratus RNFL measurements were larger than Cirrus-OCT, but smaller when average RNFL thickness was very thin (<= 56 mu). Conclusions Although the Cirrus-OCT and Stratus-OCT RNFL thickness measurements are well correlated in patients with optic neuritis, RNFL measurements cannot be directly compared. Clinicians should be aware that measurements are generally higher with Stratus-than with Cirrus-OCT. Eye (2011) 25, 233-238; doi:10.1038/eye.2010.206; published online 24 December 2010