Comparison of retinal thickness in normal eyes using Stratus and Spectralis optical coherence tomography

Spectral-domain optical coherence tomography (SD-OCT) is an advancement over time-domain OCT (TD-OCT) in the imaging of retinal disorders. Retinal thickness measured by SD-OCT differs from that measured by TD-OCT because the delineation of the outer boundary of the retina differs in the two instruments. The present study aims to evaluate this difference by comparing macular thickness, as obtained by Stratus and Spectralis OCT, in subjects without any known retinal disease.

Thirty-six subjects with no history of retinal disease and with normal vision and normal intraocular pressure were enrolled in the study. Both Stratus and Spectralis OCT scanning were performed by the same operator on all subjects in one eye. Central point thickness (CPT) and retinal thickness in nine ETDRS subfields, including central subfield (CSF), were measured. Student's t-test was used to determine statistical significance.

Mean CPT, as measured by the Stratus and Spectralis OCT, was 166.9 +/- 20.9 microm and 225.1 +/- 17.1 microm (P < 0.0001), and mean CSF was 202.3 +/- 19.6 microm and 271.4 +/- 19.6 microm (P < 0.0001), respectively. Although the mean difference in CSF thickness was 69.1 microm, it ranged from 61.9 to 74 microm in the other eight ETDRS subfields.

An increased measurement in retinal thickness of approximately 65 to 70 microm, as measured by Spectralis OCT compared with Stratus OCT, is consistent with the extent of axial retinal thickness measured by the two instruments. This increased measurement corresponds to the inclusion of the outer segment-RPE-Bruch's membrane complex by Spectralis OCT, which is relevant to studies using the newer SD-OCT for assessment of retinal thickness.