Optical Coherence Tomographic Imaging of Sub-Retinal Pigment Epithelium Lipid

Abstract

Spectral-domain (SD) optical coherence tomography (OCT) has enhanced our ability to image the sub–retinal pigment epithelium (RPE) space in retinal disorders associated with pigment epithelial detachments (PEDs).^1-6 With serial SD-OCT imaging, greater insight into the pathogenesis and natural history of PEDs may be gained and may supplement older modalities such as fluorescein angiography (FA), indocyanine green angiography (ICGA), and histopathology specimens.^7-11 Using SD-OCT, we identified a unique finding associated with PEDs in patients with neovascular age-related macular degeneration (AMD)—the so-called onion sign. Reminiscent of the layers of an onion, this finding appears as layers of hyperreflective bands between the RPE and Bruch membrane within vascularized PEDs. Coscas¹² previously reported this OCT finding as bands of fibrovascular tissue. However, we propose that these hyperreflective bands likely represent sub-RPE lipid trapped within fibrovascular tissue that originates from type 1 neovascular exudation. Although intraretinal and subretinal lipid are commonly present in a multitude of retinal diseases including diabetic retinopathy, retinal vein occlusions, hypertensive retinopathy, Coats disease, macular telangiectasia type 1, radiation retinopathy, and Bartonella neuroretinitis, we are not aware of other conditions that commonly produce sub-RPE lipid.^13-19