Multimodal imaging features and clinical relevance of subretinal lipid globules

Purpose: To describe the presence of subretinal lipid globules (SLG), analyze the multimodal imaging features inherent in their optical properties and provide a means to distinguish them from other retinal structures and clinical signs. Design: Retrospective cohort study. Methods: The clinical data and multimodal imaging features of 39 patients (49 eyes) showing SLG were evaluated. Patients underwent color fundus photography, near-infrared reflectance (NIR), spectral-domain (SD) and swept-source (SS) optical coherence tomography (OCT) and OCT angiography. In vitro phantom models were used to model OCT optical properties of water, mineral oil, and intralipid droplets and to investigate the optical mechanisms producing hypertransmission tails beneath SLG. Results: The SLG were not visible in color fundus photographs or NIR images. With both SD- and SS-OCT B-scans, SLG appeared as 31-157 micron round hyporeflective structures demonstrating a characteristic hypertransmission tail previously described with lipid globules found in the choroid and in neovascular membranes. Similarly, with en face OCT, SLG appeared as small round hyporeflective structures. SLG were encountered most often in eyes with neovascular age-related macular degeneration (AMD) that had type 1 macular neovascularization (MNV) (91.8%). Of these eyes, 93.3% were receiving intravitreal anti-vascular endothelial growth factor (VEGF) therapy (median of 15 injections) with a mean follow-up of 52.6 months. The number of prior injections positively correlated with the number of SLG. The detection of MNV preceded the presence of SLG in 66.7% of cases. En face OCT showed that in many eyes (49%) SLG appeared in clusters of >10. In 38.8% of eyes, SLG were found overlying type 1 MNV and in 44.9% of eyes, often those with more numerous SLG, the SLG were located near the lesion border. In 2 eyes with AMD followed for nonexudative type 1 MNV, SLG were detected prior to the detection of other imaging signs of exudation. SLG were observed in several other exudative macular diseases. Phantom models demonstrated that the hypertransmission tail beneath SLG is related to a lensing effect produced by these hyporeflective spherical structures. Conclusions: SLG are a newly recognized OCT feature frequently seen in eyes receiving intravitreal anti-VEGF therapy for type 1 MNV due to AMD. OCT B-scans show SLG as small, round, hyporeflective structures with a characteristic hypertransmission tail. This OCT signature is influenced by the OCT focal plane and it relates to reduced signal attenuation through oil and a lensing effect created by a higher refractive index compared to surrounding tissue.