Abstract
Purpose: :
To assist clinicians in their ability to identify buried disc drusen (DD) with Spectral Domain Optical Coherence Tomography (SDOCT) in patients with irregular optic nerve (ON) borders or a bulging, hyperemic appearance. To explore additional modalities for evaluating the drusenous disc for papilledema, glaucoma (glc) and other non-glaucomatous optic neuropathies.
Methods: :
SDOCTs of the ON were obtained in a patient with onesurfacing DD to identify the appearance of this DD and others on SDOCT. B-scan ultrasonography was utilized to confirm the presence of DD. Additional scans in multiple patients with confirmed buried DD were obtained for comparison. Optic Blood Flow Analysis (OBF), Fundus Autofluorescence (FAF), and GDx with progression analysis were all utilized to evaluate ON integrity. To rule out papilledema, morphology of the peripapillary RPE was considered.1
Results: :
DD appear as rounded hyporeflectant areas on SDOCT with a fine hyperreflective anterior border. They create less shadowing than blood vessels, their borders are denser than cysts’, and they are finite on consecutive scans. These discrete structures were found at various depths within ON heads (ONH) with confirmed buried DD. Superficial DD were identified with FAF. GDx &/or SDOCT identify progressive RNFL thinning in some cases, but etiology may be due to DD or to normal tension glc. In one patient with pigmentary dispersion syndrome, probable glc and DD, OBF was paradoxical (i.e., increased CO2 led to vascular constriction).
Conclusions: :
Buried DD complicate the clinical ability to rule out various ON disorders, including papilledema. SDOCT affords clinicians new non-invasive opportunities to probe below the surface of the ON. The hyporeflective appearance of DD may not be anticipated by clinicians, as B-scans show calcified drusen as hyperreflective on echo. In patients with RNFL defects, SDOCT may be used to identify the presence of buried DD in the corresponding aspect of the ONH. Visual field loss may be due to axonal bearing on DD or to glc. As both glc and DD may cause progressive RNFL loss, this cannot be considered a differential. OBF may be atypical in cases of DD, warranting further study. As OCT detects changes in optical reflectivity, it is hypothesized that DD are dense and homogenous, resulting in hyperreflective borders with hyporeflectant centers. SDOCT may be more useful in those patients with buried DD which are not calcified and do not exhibit FAF, since B-scan often contributes little in such cases, and deep DD typically do not autofluoresce. 1 Sibony P, Kupersmith MJ, Rohlf FJ. Shape analysis of the peripapillary RPE layer in papilledema and ischemic optic neuropathy. Invest Ophthalmol Vis Sci. 2011 Oct 10;52(11):7987-95.
Keywords: imaging/image analysis: clinical • optic disc • clinical (human) or epidemiologic studies: outcomes/complications