Differentiation between optic disc drusen and optic disc oedema using fundus photography

Purpose To describe a funduscopic sign that can be used to differentiate between optic disc drusen ( ODD ) and optic disc oedema ( ODE ). Methods A total of 73 eyes from 73 consecutive subjects with disc margin blurring who had been evaluated using spectral‐domain optical coherence tomography ( SD ‐ OCT ) were included. Final diagnosis was made by SD ‐ OCT ; ODD was defined by direct visualization of ODD , while ODE was defined by documentation of retinal nerve fibre layer oedema (nasal retinal nerve fibre layer thickness >78.0 μm). Peripapillary retina was selected as a two‐disc‐diameter‐sized square image from the fundus photograph. Using MATLAB software, colour photographs were converted to indexed image of eight colours. Presence of a smooth contour strip between the nasal disc margin and juxtapapillary retina was defined as a halo. Whether the halo could predict the ODD was analysed retrospectively. Results The halo sign was detected in 45 eyes (100%) with ODD including one eye with both ODD and ODE. No eyes with ODE alone showed the halo sign. The halo sign implied the presence of ODD (Cohen's kappa = 1.000, p   <   0.001) and the absence of ODE (Cohen's kappa = 0.971, p   <   0.001). The halo sign showed a good interobserver reliability [ ICC (2, 1) = 0.944, 95% confidence interval 0.912–0.964]. SD ‐ OCT images showed that halos represented retinal elevations above ODD . Conclusions In the patients with blurred disc margin, the presence of a halo strongly suggested underlying ODD rather than ODE .