Repeatability of Foveal Measurements Using Spectralis Optical Coherence Tomography Segmentation Software

Abstract

Purpose: To investigate repeatability and reproducibility of thickness of eight individual retinal layers at axial and lateral foveal locations, as well as foveal width, measured from Spectralis spectral domain optical coherence tomography (SD-OCT) scans using newly available retinal layer segmentation software.

Methods: High-resolution SD-OCT scans were acquired for 40 eyes of 40 young healthy volunteers. Two scans were obtained in a single visit for each participant. Using new Spectralis segmentation software, two investigators independently obtained thickness of each of eight individual retinal layers at 0°, 2° and 5° eccentricities nasal and temporal to foveal centre, as well as foveal width measurements. Bland-Altman Coefficient of Repeatability (CoR) was calculated for inter-investigator and inter-scan agreement of all retinal measurements. Spearman's ρ indicated correlation of manually located central retinal thickness (RT0) with automated minimum foveal thickness (MFT) measurements. In addition, we investigated nasal-temporal symmetry of individual retinal layer thickness within the foveal pit.

Results: Inter-scan CoR values ranged from 3.1 μm for axial retinal nerve fibre layer thickness to 15.0 μm for the ganglion cell layer at 5° eccentricity. Mean foveal width was 2550 μm ± 322 μm with a CoR of 13 μm for inter-investigator and 40 μm for inter-scan agreement. Correlation of RT0 and MFT was very good (ρ = 0.97, P < 0.0005). There were no significant differences in thickness of any individual retinal layers at 2° nasal compared to temporal to fovea (P > 0.05); however this symmetry could not be found at 5° eccentricity.

Conclusions: We demonstrate excellent repeatability and reproducibility of each of eight individual retinal layer thickness measurements within the fovea as well as foveal width using Spectralis SD-OCT segmentation software in a young, healthy cohort. Thickness of all individual retinal layers were symmetrical at 2°, but not at 5° eccentricity away from the fovea.

Fig 1. 1a and b.

Central retinal thickness and layer segmentation by Spectralis SD-OCT software. The Spectralis software displays overall retinal thickness as the vertical distance between the vitreoretinal interface and Bruch’s membrane. Using the thickness profile, the foveal reflex was bisected by the software caliper, and the thickness of the individual layers was recorded in microns (a). Segmentation of the individual retinal layers can be seen in the lower image (b).

Fig 2. Positioning of software caliper for lateral retinal thickness measurement.

Fig 3. a and b.

Measurement of foveal width. Maximum retinal thickness nearest to the foveal reflex on nasal (a) and temporal side identified from the thickness profile. Foveal width was measured in microns using the inbuilt manual calipers (b).

Fig 4. a-d.

Bland-Altman plots to show a) Inter-observer agreement of central retinal thickness; b) Inter-scan agreement of central retinal thickness; c) Inter-observer agreement of foveal width; d) Inter-scan agreement of foveal width. All measurements presented in microns. Red line indicates mean difference, d between values. Limits of Agreement (d+1.96s) represented by upper and lower grey dashed lines respectively.