Reproducibility of SD-OCT-Based Ganglion-Cell-Complex-Layer Thickness in Early Glaucoma using Commercial and Custom Segmentation Algorithms

Abstract

 

Purpose

 

To compute the reproducibility of SD-OCT-based ganglion-cell-layer plus inner-plexiform-layer (GCL+IPL) thickness measurements from both a commercially available algorithm (Cirrus, Carl Zeiss Meditec, Inc.) and a custom-developed algorithm (from the suite of Iowa Reference Algorithms) in early glaucoma patients.

 

Methods

 

Macula SD-OCT volumes (Cirrus, Carl Zeiss Meditec, Inc., Dublin, CA, 200 x 200 x 1024 voxels, 6 x 6 x 2 mm³) were obtained prospectively in both eyes of 58 patients with open-angle glaucoma or glaucoma suspicion on two separate visits. The visits were at most four months apart. The combined GCL+IPL thickness was computed for each SD-OCT volume within an elliptical annulus centered at the fovea (with a vertical inner and outer radius of 0.5 mm and 2.0 mm, respectively; and horizontal inner and outer radius of 0.6 mm and 2.4 mm, respectively) based on two algorithms: (1) a previously published graph-theoretic layer segmentation approach developed at The University of Iowa and (2) the Ganglion Cell Analysis module of version 6 of the Zeiss Cirrus software. The mean overall thickness in the elliptical annulus was computed as well as the thickness within six sectors (Figure 1). For statistical analysis, the SD-OCT volumes of twelve eyes were excluded because of a low signal strength (≤ 5), image acquisition errors, or errors in performing the commercial GCL+IPL analysis in at least one of the repeat acquisitions.

 

Results

 

From the 104 analyzed eyes with repeated measurements, the intraclass correlation coefficient (ICC) for the overall elliptical annular GCL+IPL thickness was 0.98 (95% CI 0.97, 0.99) using the Iowa algorithm and 0.95 (0.93, 0.97) using the Cirrus algorithm; the intervisit standard deviation (SD) was 1.63 μm (Iowa) and 2.52 μm (Cirrus); and the coefficient of variation (CV) was 2.3% (Iowa) and 3.6% (Cirrus). The sector-based ICCs, intervisit SDs, and CVs are reported in Table 1. The ICCs were significantly higher using the Iowa approach except for Region S where there was no difference in the reproducibility.

 

Conclusions

 

SD-OCT-based ganglion cell thickness measurements in early glaucoma patients are highly reproducible.

 

 

Figure 1. (A) Central B-scan from example volume and (B) corresponding Iowa layer segmentation. (C) Example SD-OCT projection image and (D) six sectors for regional GCL+IPL analysis.

 

 

Table 1.

 

Keywords: 550 imaging/image analysis: clinical • 531 ganglion cells • 629 optic nerve