Buried Disc Drusen Have Hypo-Reflective Appearance on SD-OCT

Abstract

Buried disc drusen are an important differential diagnosis for papilledema. Spectral domain optical coherence tomography (SD-OCT) affords clinicians with new non-invasive opportunities to probe below the surface of the optic nerve. Clinicians may use the knowledge of this appearance to rule out buried disc drusen in patients with irregular optic nerve borders or a bulging, hyperemic appearance. SD-OCTs were obtained in a patient with one surfacing disc druse, identifying the nature of the appearance of this disc druse and others in this and the contralateral eye when imaged with this technology. B-scan ultrasonography was used to confirm the presence of disc drusen. Additional scans in multiple patients with confirmed buried drusen were obtained for comparison. Drusen appear as rounded hyporeflectant areas on SD-OCT, similar in appearance to blood vessels. They share the appearance of cysts but show a fine hyperreflective border anteriorly. These same discrete hyporeflective areas were found at various depths within optic nerve heads with confirmed buried disc drusen. The hyporeflective appearance may not be anticipated by clinicians, as B-scans show calcified drusen as hyperreflective on echo. It is hypothesized that the hyporeflectant appearance of drusen is due to a constancy in refractive index through the druse, as OCT detects changes in optical reflectivity. Thus, drusen are likely dense and homogenous. SD-OCT may be more useful in those patients with buried disc drusen which are not calcified as B-scan often contributes little in such cases.