Abstract
To update the recommended guidelines when quantifying choriocapillaris (CC) flow deficits (FDs) in eyes with age-related macular degeneration (AMD) using swept-source optical coherence tomography angiography (SS-OCTA).
Evidence-based perspective.
Review of literature and experience of authors.
A current challenge when quantifying CC FDs using SS-OCTA is the implementation of an objective compensation strategy to adjust for the signal attenuation arising under drusen in eyes with AMD. Our previous compensation strategy was used as a general approach to adjust for the OCTA signal attenuation associated with most drusen. However, the variability of the OCTA signal loss under drusen necessitated a more objective strategy that could be tailored to each case. We propose a compensation strategy using a parameter gamma (γ) that allows for the selection of an appropriate compensation level. The optimal γ value is identified as the one producing the most homogeneous OCT signal across the whole CC structural slab. This approach minimizes the possibility that areas of decreased flow in the compensated CC flow image might reflect drusen-related or compensation-related artifacts rather than true deficits. Additional lesions that present unique challenges when quantifying CC FDs include the presence of choroidal hypotransmission defects (hypoTDs) caused by calcified drusen (CaD) and hyperreflective foci (HRF) as well as choroidal hypertransmission defects (hyperTDs) caused by foci of atrophy. We recommend identifying and outlining these regions on an en face sub-retinal pigment epithelium (subRPE) slab with segmentation boundaries between 64 and 400 µm beneath Bruch's membrane (BM). The hypoTDs should be excluded from CC quantification because of the lack of significant OCTA signal, while the hyperTDs should be excluded from being compensated because doing so can artifactually increase the percentage of CC FDs.
The analysis of CC FDs in AMD requires special attention to drusen, hypoTDs, and hyperTDs to avoid introducing artifacts. By properly adjusting the compensation levels under drusen and adjusting the quantification of CC FDs by accounting for hyperTDs and hypoTDs, researchers interested in measuring CC FDs in AMD can have greater confidence in their measurements, particularly when investigating the role of CC flow impairment in AMD progression.