Enhanced OCT reveals new characteristics of optic disc drusen

In this retrospective study, deeper-penetration OCT imaging revealed the internal characteristics of optic disc drusen and their relationship with the lamina cribrosa in vivo. It found that optic nerve drusen often contain hyper-reflective foci and are typically located anterior to the lamina cribrosa.

Previous studies have evaluated the use of time-domain and spectral-domain OCT for detecting optic disc drusen and were limited by the fact that these OCT modalities are unable to visualize the complete depth of the prelaminar optic nerve posterior to the level of the retinal pigment epithelium. This study is limited by its retrospective nature but otherwise demonstrates superlative imaging of optic disc drusen at all depths of the optic disc. Enhanced depth imaging (EDI)-OCT, if widely available to the practicing ophthalmologist, would be helpful in detecting buried optic disc drusen in patients with elevated optic discs.

The authors reviewed the charts of 15 patients (26 eyes) with optic nerve disc drusen who were examined using EDI-OCT, swept source OCT, and fundus autofluorescence.

EDI-OCT and swept source OCT showed multiple optic disc drusen at different levels, with most located immediately anterior to the lamina cribrosa. The drusen were ovoid regions of lower reflectivity bordered by hyper-reflective material, and in 12 eyes there were internal hyper-reflective foci.

The mean diameter of the optic disc drusen as measured in OCT images was 686.8 μm. Both OCT and autofluorescence imaging showed an inverse correlation between the size of the optic nerve drusen and the retinal nerve fiber layer thickness. The presence of intralesional hyper-reflective foci seen with OCT also was correlated with a thinner nerve fiber layer thickness.

The authors write that the autofluorescence found in optic disc drusen could be the result of the large number of mitochondria they contain. Future studies should include proteomic analysis and evaluation to ascertain if the autofluorescence seen clinically co-localizes with mitochondrial aggregates.

They conclude that the novel aspect of optic nerve drusen demonstrated in vivo is the limited range of the scleral canal in which they are found. The findings suggest that axonal loss could lead to abnormal deposition of mitochondria and protein in susceptible individuals. Increasing size of the drusen could further compromise the remaining nerve fibers within the scleral canal, with a potential for a self-reinforcing cycle in eyes with optic nerve drusen.