Comparison of Two Different OCT Systems: Retina Layer Segmentation and Impact on Structure-Function Analysis in Glaucoma

Figure 1

Top: (a) example from Early Treatment Diabetic Retinopathy Study (ETDRS) grid taken from Spectralis printout, used to calculate MT in both OCTs: scan area of 6 × 6 mm, divided into three concentric circles with 1 mm, 3 mm, and 6 mm diameter, respectively. Here, we used values from the 1 and 3 mm circles of the grid. (b) Area used in Cirrus to calculate GCIPL thickness corresponding to an elliptical annulus with a 2.0 mm vertical and 2.4 mm horizontal radius, excluding a central elliptical area (0.5 mm vertical and 0.6 mm horizontal radius) that corresponded to the foveola; in Spectralis GCIPL thickness was calculated with values in the 3 mm circle from ETDRS grid, excluding the 1 mm diameter circle. Bottom: OCT images using layer segmentation software from each instrument: (c) Spectralis, (d) Cirrus (same patient). While Cirrus software calculates only ganglion cell-inner plexiform layer (GCIPL) and excludes retina nerve fiver layer (RNFL), Spectralis software segments all retina layers and values from ganglion cell and inner plexiform layers were added manually. The white bar represents limits for thickness measurement of ganglion cell-inner plexiform layer in Spectralis (left) and Cirrus (right).

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