Macular thickness measurements in normal eyes with time-domain and Fourier-domain optical coherence tomography

Abstract

Purpose: To compare macular thickness measurements using time-domain optical coherence tomography (OCT) and Fourier-domain OCT.

Methods: Thirty-two eyes from 32 normal patients underwent complete ophthalmic evaluation. Macular scanning using the StratusOCT and the RTVue-100 OCT were performed for a total of three times each on the same visit. The average retinal thicknesses of the nine macular sectors as defined by the Early Treatment Diabetic Retinopathy Study, along with the foveal center point and macular volume, were recorded. The SD, the coefficient of variation, and the intraclass correlation coefficient were calculated for each parameter studied. Comparisons were made between the two OCTs in terms of retinal thicknesses measurements, their reproducibility, and macular regional differences. Correlations between retinal thickness and demographic variables (age and gender) were also investigated. Due to known differences in segmentation algorithms of the two OCTs, software calipers were used to measure the distance from the internal limiting membrane to the photoreceptor inner segment-outer segment junction at the foveal center point on all RTVue scans to allow a more fair comparison.

Results: The RTVue yielded greater retinal thickness measurements in nearly all macular subfields compared with the StratusOCT. Even after accounting for differences in segmentation algorithms, significant disparities were still evident with the RTVue measurements less than those of the StratusOCT at the foveal center. On both machines, the macula was thinnest at the fovea and thickest within the 3 mm ring. There were some consistent regional variations in macular thickness evident on both OCTs. Compared with the StratusOCT, the RTVue generally had lower coefficients of variation and higher intraclass coefficients, suggesting better reproducibility. Age and gender also appeared to be important determinants in some macular thickness parameters.

Conclusion: Compared with StratusOCT, the RTVue fourier-domain OCT yields greater retinal thickness measurements with greater reproducibility, presumably due to different segmentation algorithms, increased sampling density, and greater resolution. However, regional differences across the macula can be consistently observed with both devices.

Conflict of interest statement

Conflict of Interest: Dr. Sadda is a co-inventor of Doheny intellectual property related to optical coherence tomography that has been licensed by Topcon Medical Systems and is a scientific advisory board member for Heidelberg Engineering. Both companies manufacture devices that may compete directly with the devices discussed in this manuscript.

Figures

Figure 1

The Early Treatment of Diabetic Retinopathy Study (ETDRS) macular map sectors. The four quadrants of the outer, 6mm diameter ring around the fovea are labeled S6, T6, I6, and N6 to represent the superior, temporal, inferior, and nasal regions, respectively. The inner, 3mm diameter ring is labeled analogously. C1 represents the innermost 1mm diameter ring around the fovea.

Figure 2

Boxplot of macular thickness (ETDRS map sectors, see Figure 1). The retinal thicknesses ± standard deviation, as measured by the StratusOCT and the Fourier-domain OCT for a particular region, are plotted next to each other for comparison.

Figure 3

The Early Treatment of Diabetic Retinopathy Study (ETDRS) macular grid is shown depicting regional differences in retinal thickness between the RTVue-100 and the StratusOCT. The RTVue-100 generally yielded thicker (positive percentage) measurements.