2.3. Spectral domain OCT imaging

We used Heidelberg Spectralis spectral domain OCT to perform two protocols of each eye for each patient: (1) central retina (macula) dense horizontal scanning; central 20 × 20° area; 49 b-scans (averaging 15 frames per b-scan); 512 a-scans per b-scan and (2) axonal ring scan around the optic nerve head for RNFL (8 frames averaged). Peripapillary RNFL was measured in six sectors provided by the Heidelberg software (temporal superior, nasal superior, nasal, nasal inferior, temporal inferior, and temporal). Macular thickness was measured in the Early Treatment of Diabetic Retinopathy Study map (fovea [Ø 1 mm] and the mean of four quadrants of both the inner ring [Ø 1-3 mm], area 2 to 5, and the outer ring [Ø 3-6 mm], area 6 to 9) (Fig. 1). In the fovea, the inner and the outer ring segmentation analysis was performed with the Heidelberg segmentation software (version 1.9.204.0) to calculate thickness of the following retinal layers: RNFL, ganglion cell layer (GCL), and inner plexiform layer (IPL) (Fig. 1).

Overview of retinal imaging cohort. Overview of the retinal imaging cohort that included retinal thickness measurements using optical coherence tomography (OCT) imaging of the optic nerve head and macula and visual rating scores for cortical atrophy on magnetic resonance imaging (MRI).