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Sri Krishna Mukkamala, Rogerio A. Costa, Adrian Fung, K Bailey Freund; Optical Coherence Tomography Imaging of Sub - Retinal Pigment Epithelium Lipid. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2643.
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To describe a novel optical coherence tomography (OCT) finding believed to represent sub-retinal pigment epithelium (RPE) lipid-rich material, in which layered hyper-reflective bands beneath the RPE, reminiscent of the layers of an onion, were observed.
Retrospective observational case series. Clinical histories of 14 patients (15 eyes) with "the onion sign" were reviewed. Imaging studies analyzed included spectral domain OCT (SD-OCT), color and red free (RF) photographs, near infrared reflectance (NIR), fundus autofluorescence (FAF), and blue light FAF (bFAF) images.
15 eyes of 14 patients manifested sub-RPE hyper-reflective bands. There were 12 women and 2 men. Mean patient age was 77 years (range, 60-92 years). Best-corrected Snellen visual acuity ranged from 20/25 to count fingers with a median visual acuity of 20/60. One of 14 patients had a bilateral "onion sign" and 3 of 16 eyes had multifocal "onion signs" in the same eye. All eyes had neovascular age-related macular degeneration (NV-AMD) with type 1 (sub-RPE) neovascularization. In all patients, the "onion sign" correlated with areas of yellowish exudates seen clinically that appeared bright on both RF and NIR imaging but more so on NIR. No specific bFAF or FAF pattern was observed.
The "onion sign" refers to layered hyper-reflective bands in the sub-RPE space usually associated with chronic exudation from type 1 neovascularization in patients with AMD. With an associated bright NIR, these bands may correspond to lipid, collagen, and fibrin. Since the "onion sign" co-localizes to areas of exudation that are known to be composed of lipoprotein, we propose that this finding represents layers of precipitated lipid in the sub-RPE space.
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