Retinal imaging with fundus photography and spectral-domain OCT

All subjects underwent fundus photography and spectral-domain optical coherence tomography (OCT) on the same day. For both examinations, the pupils were dilated using tropicamide 1%. Two fundus photographs of each eye, the first centred on the optic disc and the second centred on the fovea, were acquired using a 45° fundus camera (Visucam^NM/FA, Carl Zeiss Meditec, Jena, Germany). Spectral-domain OCT (Spectralis HRA HROCT; Heidelberg Engineering GmbH, Dossenheim, Germany) was used to obtain circular scans (3.4 mm in diameter) centred at the optic disc and horizontal, vertical-B, and volume scans of the macular area. The volume scans contained 49 sections (with spacing of 120 μm) of a 20 × 20° area of the macula. Bilateral fundus photographs and OCT images were available for 1503 of the 1508 subjects (5 subjects underwent examination of the fundus of only one eye because of media opacity).

A localised RNFLD was defined as a dark wedge-shaped area with a connecting optic disc border on fundus photography that had a width or length of 5°–45°^9,26, which was confirmed on OCT as an abruptly dropped contour line on the RNFL thickness profile (Fig. 1). The images of the fundus were assessed by an ophthalmologist (JYS) who was blinded to all subject data except for the fundus photographs and OCT images. To determine the inter-observer variability, photographs of 100 randomly selected subjects were reviewed by two blinded ophthalmologists (JYS, SHB) working independently of each other. The coefficient for inter-observer variability in detection of localised RNFLDs was 0.99. RNFLDs associated with significant glaucomatous changes at the optic disc, chorioretinal scarring, a history of uveitis, or retinal artery or vein occlusion were not regarded as localised RNFLDs in the analysis.

Localised retinal nerve fibre layer defect assessed using fundus photography (a) and spectral-domain optical coherence tomography (b). A localised retinal nerve fibre layer defect was defined as a dark wedge-shaped area with a connecting optic disc border on fundus photography that had a width or length of 5°–45° (a), which was confirmed on optical coherence tomography as an abruptly dropped contour line on the thickness profile of the retinal nerve fibre layer (b).