Systematic quantification of outer retinal morphology in three different SD-OCT devices in geographic atrophy

To define interdevice differences in quantitative outer retinal biomarkers across three spectral-domain (SD) optical coherence tomography (OCT) devices in geographic atrophy (GA).

Patients with GA prospectively underwent imaging using Spectralis (Heidelberg Engineering), Cirrus (Zeiss) and Maestro (Topcon) OCT devices. Ellipsoid zone (EZ) and outer nuclear layer (ONL) thickness, as well as EZ and retinal pigment epithelium (RPE) loss, were automatically pre-segmented and manually corrected. Quantitative measurements were compared between OCT devices using anova or Friedman tests. Bland-Altman analysis determined mean differences and 95% limits of agreement (LoA).

A total of 7080 B-scans from 120 OCT volumes of 40 eyes were analysed. Mean patient age was 80 ± 7 years. Mean EZ thickness in the 6-mm macular cube was 34.8 ± 4.6, 33.4 ± 4.1 and 31.0 ± 4.8 μm for Spectralis, Cirrus and Maestro, respectively, while mean ONL thickness was 77.8 ± 9.2, 78.5 ± 9.4 and 75.8 ± 9.6 μm. Interdevice differences were significant for EZ and ONL-thickness (all p < 0.05). Mean EZ thickness bias ranged from 1.5 to 3.8 μm, with the widest LoA between Spectralis and Maestro. Mean ONL-thickness bias ranged from -0.7 to 2.7 μm, with the widest LoA between Cirrus and Maestro. EZ-loss and EZ/RPE-loss-area also differed significantly (both p < 0.01).

Visualization and quantification of atrophic features at the level of the photoreceptors, including EZ thickness, EZ loss and ONL thickness, are influenced by the implemented OCT machine. Consistency in the OCT device during patient monitoring allows for the highest precision and eliminates interdevice differences in quantitative outcome measures.