Utility of Spectral-Domain Optical Coherence Tomography in Differentiating Papilledema From Pseudopapilledema: A Prospective Longitudinal Study.

BACKGROUND: Prospective and longitudinal studies assessing the utility of spectral-domain optical coherence tomography (SD-OCT) to differentiate papilledema from pseudopapilledema are lacking. We studied the sensitivity and specificity of baseline and longitudinal changes in SD-OCT parameters with 3D segmentation software to distinguish between papilledema and pseudopapilledema in a cohort of patients referred for evaluation of undiagnosed optic disc elevation. METHODS: Fifty-two adult patients with optic disc elevation were enrolled in a prospective longitudinal study. A diagnosis of papilledema was made when there was a change in the appearance of the optic disc elevation on fundus photographs as noted by an independent observer at or before 6 months. The degree of optic disc elevation was graded using the Frisen scale and patients with mild optic disc elevation (Frisen grades 1 and 2) were separately analyzed. SD-OCT parameters including peripapillary retinal nerve fiber layer (pRNFL), total retinal thickness (TRT), paracentral ganglion cell layer-inner plexiform layer (GCL-IPL) thickness, and optic nerve head volume (ONHV) at baseline and within 6 months of follow-up were measured. RESULTS: Twenty-seven (52%) patients were diagnosed with papilledema and 25 (48%) with pseudopapilledema. Among patients with mild optic disc elevation (Frisen grades 1 and 2), baseline pRNFL (110.1 µm vs 151.3 µm) and change in pRNFL (ΔpRNFL) (7.3 µm vs 52.3 µm) were greater among those with papilledema. Baseline and absolute changes in TRT and ONHV were also significantly higher among patients with papilledema. The mean GCL-IPL thickness was similar at baseline, but there was a small reduction in GCL-IPL thickness among patients with papilledema. Receiver operator curves (ROCs) were generated; ΔpRNFL (0.93), ΔTRT (0.94), and ΔONHV (0.95) had the highest area under the curve (AUC). CONCLUSIONS: The mean baseline and absolute changes in SD-OCT measurements (pRFNL, TRT, and ONHV) were significantly greater among patients with papilledema, and remained significantly greater when patients with mild optic disc elevation were separately analyzed. ROCs demonstrated that ΔpRNFL, ΔTRT, and ΔONHV have the highest AUC and are best able to differentiate between papilledema and pseudopapilledema.

Polarized super-resolution structural imaging inside amyloid fibrils using Thioflavine T.

Thioflavin T (ThT) is standardly used as a fluorescent marker to detect aggregation of amyloid fibrils by conventional fluorescence microscopy, including polarization resolved imaging that brings information on the orientational order of the fibrils. These techniques are however diffraction limited and cannot provide fine structural details at the fibrils scales of 10-100 nm, which lie beyond the diffraction limit. In this work, we evaluate the capacity of ThT to photoswitch when bound to insulin amyloids by adjusting the redox properties of its environment. We demonstrate that on-off duty cycles, intensity and photostability of the ThT fluorescence emission under adequate buffer conditions permit stochastic super-resolution imaging with a localization precision close to 20 nm. We show moreover that signal to noise conditions allow polarized orientational imaging of single ThT molecules, which reveals ultra-structure signatures related to protofilaments twisting within amyloid fibrils.