Advances in quantifications of outer retinal layers in geographic atrophy comparing High-Res and conventional SPECTRALIS optical coherence tomography

Abstract

Purpose : Quantification of distinct biomarkers in optical coherence tomography (OCT) becomes more important in geographic atrophy (GA) due to promising therapeutic options in the near future. The purpose of this study was to investigate differences between standard and advanced devices with varying axial resolution in outer retinal layer segmentations in GA.

Methods : The novel investigational high resolution OCT (High-Res OCT) uses a shorter central wavelength and a broader spectrum to provide an axial resolution of up to 3µm compared to 7µm in conventional OCT imaging (SPECTRALIS HRA+OCT). GA patients fulfilling complete retinal pigment epithelium (RPE) and outer retinal atrophy (cRORA) criteria were imaged with both devices (both from Heidelberg Engineering, Heidelberg, Germany) using a 20°x20° scan pattern. The RPE, photoreceptor (PR) layer consisting of the ellipsoid zone and interdigitation zone, and external limiting membrane (ELM) were segmented in 49 B-Scans/OCT using artificial intelligence-based automated segmentation followed by manual corrections (Fig. 1). Subretinal drusenoid deposits (SDD) were captured between the RPE and PR layers. Layer thickness and loss as well as SDD volume were computed and compared between devices using a mixed effect model.

Results : Ten eyes from 9 patients with GA were included. The RPE was significantly thinner with a mean thickness of 15.70µm (95%CI 14.59–16.81) in High-Res OCT compared to 21.58µm (95%CI 20.46–22.69) in conventional OCT (p<0.001). However, no significant difference in the area of RPE loss was found (p=0.125). The PR layer was significantly thicker in the High-Res OCT (26.49µm (95%CI 23.73–29.25) compared to 25.00µm (95%CI 22.24–27.76) in the conventional OCT, p=0.03). The area of PR loss appeared larger in the conventional than in the High-Res device (p<0.001). ELM loss was lower in the High-Res OCT (p=0.009). No significant difference in SDD volume was found between devices (p=0.154).

Conclusions : High-Res OCT with superior axial resolution is able to identify outer retinal layers with higher precision due to the retina’s highly organized structures. Differences were found for layer thickness and loss area between devices. Higher axial resolution could help researchers adequately investigate disease pathomechanisms, progression patterns of macular atrophy and identify therapeutic targets.

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