A recent study investigated the unique optical properties of subretinal lipid globules (SLG) to pinpoint their clinical relevance and provide a means of distinguishing them from other retinal structures and clinical signs.
The retrospective cohort study included clinical data and multimodal imaging features of 49 eyes of 39 patients with SLG. The researchers used many imaging modalities, including color fundus photography, near-infrared reflectance, spectral-domain and swept-source OCT and OCT angiography. To model the OCT optical properties of water, mineral oil and intralipid droplets, the researchers used in vivo phantom models. They also investigated the optical mechanisms that produce hypertransmission tails beneath SLG.
Subretinal Lipid Globule Visibility
|OCT||31μm to 157μm round, hyporeflective structures; characteristic hypertransmission tail similar to those of lipid globules found in the choroid and neovascular membranes|
|En face OCT-A||Small, round hyporeflective structures|
|Color fundus photos||Not visible|
|NIR images||Not visible|
The researchers found that SLG were most often seen in eyes with wet AMD with Type I macular neovascularization. A majority of these eyes (93.3%) were also undergoing anti-VEGF treatment, and the researchers noted that the number of prior injections was positively correlated with the number of SLG. Furthermore, detection of macular neovascularization preceded the presence of SLG in 66.7% of cases.
As seen on en face OCT-A, nearly half of the eyes showed SLGs in clusters of more than 10. In almost 40% of eyes, SLGs were found overlying Type I macular neovascularization, and in 44.9% of eyes—those with more numerous SLGs—SLGs tended to be located near the lesion border.
Additionally, the researchers detected SLGs prior to other imaging signs of exudation in two eyes with AMD and nonexudative Type I macular neovascularization. They also observed SLGs in several other types of exudative macular diseases.
The researchers noted that according to the phantom models, the hypertransmission tail beneath SLGs is related to a lensing effect produced by the hyporeflective spherical structures.
In conclusion, the study reported that SLGs are a commonly seen feature in eyes receiving anti-VEGF therapy for Type I macular neovascularization due to AMD. SLGs also have unique imaging features, due their round, hyporeflective structures.
“This OCT signature is influenced by the OCT focal plane and it relates to a reduced signal attenuation through oil and a lensing effect created by a higher refractive index compared to surrounding tissue,” the researchers wrote in their paper.
Fernández-Avellaneda P, Freund KB, Wang RK, et al. Multimodal imaging features and clinical relevance of subretinal lipid globules. Am J Ophthalmology. September 9, 2020. [Epub ahead of print].