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

PurposeTo describe a funduscopic sign that can be used to differentiate between optic disc drusen (ODD) and optic disc oedema (ODE). MethodsA 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 >78.0m). 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. ResultsThe 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. ConclusionsIn the patients with blurred disc margin, the presence of a halo strongly suggested underlying ODD rather than ODE.