Comparison of spectral/Fourier domain optical coherence tomography instruments for assessment of normal macular thickness

Abstract

Purpose: The purpose of this study was to report normal macular thickness measurements and assess reproducibility of retinal thickness measurements acquired by a time-domain optical coherence tomography (OCT) (Stratus, Carl Zeiss Meditec, Inc., Dublin, CA) and three commercially available spectral/Fourier domain OCT instruments (Cirrus HD-OCT, Carl Zeiss Meditec, Inc.; RTVue-100, Optovue, Inc., Fremont, CA; 3D OCT-1000, Topcon, Inc., Paramus, NJ).

Methods: Forty randomly selected eyes of 40 normal, healthy volunteers were imaged. Subjects were scanned twice during 1 visit and a subset of 25 was scanned again within 8 weeks. Retinal thickness measurements were automatically generated by OCT software and recorded after manual correction. Regression and Bland-Altman plots were used to compare agreement between instruments. Reproducibility was analyzed by using intraclass correlation coefficients, and incidence of artifacts was determined.

Results: Macular thickness measurements were found to have high reproducibility across all instruments with intraclass correlation coefficients values ranging 84.8% to 94.9% for Stratus OCT, 92.6% to 97.3% for Cirrus Cube, 76.4% to 93.7% for RTVue MM5, 61.1% to 96.8% for MM6, 93.1% to 97.9% for 3D OCT-1000 radial, and 31.5% to 97.5% for 3D macular scans. Incidence of artifacts was higher in spectral/Fourier domain instruments, ranging from 28.75% to 53.16%, compared with 17.46% in Stratus OCT. No significant age or sex trends were found in the measurements.

Conclusion: Commercial spectral/Fourier domain OCT instruments provide higher speed and axial resolution than the Stratus OCT, although they vary greatly in scanning protocols and are currently limited in their analysis functions. Further development of segmentation algorithms and quantitative features are needed to assist clinicians in objective use of these newer instruments to manage diseases.

Fig 1

Nine regions of ETDRS map. All scans produce maps consisting of 1, 3, and 6 mm diameter concentric circles (a) except for the RTVue MM5, whose outer circle is 5 mm in diameter (b). Regions 2–5 comprise the parafoveal ring, while regions 6–9 comprise the perifoveal ring.

Fig 2

Demonstration of error types, including errors in segmentation of inner retina (a); outer retina (b); out-of-register, inner, and outer retina scan error (c); cut-edge artifact (d); and off-center fixation error causing inaccurate foveal thickness measurement shown before (e) and after manual correction (f).

Fig 3

Bland-Altman plots of central subfield thickness, displayed as the difference between Cirrus HD-OCT (a); RTVue-100 MM5 (b); RTVue-100 MM6 (c); 3D OCT-1000 Radial (d); 3D OCT-1000 3D Macular (e) and Stratus OCT versus the average of the 2 measurements. Lines indicating average mean difference with 95% confidence limits are shown.

Fig 4

Regression plots of central subfield thickness measured using Cirrus HD-OCT (a); RTVue-100 MM5 (b); RTVue-100 MM6 (c); 3D OCT-1000 Radial (d); 3D OCT-1000 3D Macular (e) compared to Stratus OCT. The differences in y-intercepts reflect differences in measurement algorithms.

Fig 5

Demonstration of macular thickness segmentation algorithms in different instruments. All instruments define the inner boundary as the internal limiting membrane, but there is variation in outer boundaries. Stratus OCT measures to the IS/OS junction (a), Cirrus HD-OCT (b) and RTVue-100 (c) both measure close to the RPE, and the RTVue also draws a boundary at the inner plexiform layer. 3D OCT-1000 measures to the photoreceptor outer segment tips (d), shown as the third line from the top. This instrument also draws boundaries at the IS/OS junction (second line) and posterior RPE boundary (fourth line), which are not included in retinal thickness measurements.