Comparison of Geographic Atrophy (GA) Area Measurement from Multiple Imaging Modalities

Abstract

Purpose : To evaluate the correlation between the area measurements of geographic atrophy derived from optical coherence tomography OCT en face images from two different spectral domain (SD)-OCT devices (Cirrus vs Spectralis) versus Fundus Autofluorescence (FAF).

Methods : This was a retrospective, cross-sectional study of 84 eyes with GA in patients with AMD who were enrolled in the Amish Eye Study. Eyes were imaged with blue-light FAF (Spectralis HRA+OCT) and two spectral domain OCT devices (6x6mm volumes; 97 B-scans for the Spectralis and 128 B-scans for the Cirrus) to calculate GA measurements per CAM criteria. For FAF calculations, certified reading center graders used validated planimetric grading tools to manually outline the borders on the FAF images of all areas of definite decreased autofluorescence (DDAF) corresponding to GA. For Cirrus calculations, regions of atrophy were initially delineated automatically by the instrument software on en face OCT images (slab at the level of the choroid), and then segmentation errors were corrected manually by reading center certified graders before the calculation of the GA area. For Spectralis calculations, the regions of atrophy were calculated manually in a similar fashion to those for Cirrus, except for the absence of initial automated software delineation. Forty-four eyes had to be excluded from analysis, primarily because the GA lesion extended beyond the OCT scan area.

Results : The mean GA area as measured from the Cirrus en face OCT (n=40) was 3.38±4.27 mm²; the Spectralis en face OCT measurement was 4.38±5.28 mm² (n=40); and the DDAF (n=40) measured GA was 4.75±5.98 mm². No statistical significant differences were found between Spectralis vs FAF (p=0.775), but statistically significant differences were found between: Cirrus vs DDAF (p=0.002) and Spectralis vs Cirrus (p<0.001). Despite the differences in numerical measurements, pairwise correlations demonstrated strong and significant correlations among the modalities: Cirrus vs DDAF (r=0.973, p<0.001), Spectralis vs DDAF (r=0.976, p<0.001), Spectralis vs Cirrus (r=0.98, p<0.001).

Conclusions : Although the values are correlated, the measurement of GA area can vary depending on imaging modality, even between two SD-OCT devices, highlighting that measurements from the devices cannot be used interchangeably. The sources of variation among modalities warrants further study.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.