Relationship Between Geographic Atrophy Expansion Rate and Density of Choriocapillaris Flow Voids Using OCT Angiography

Abstract

Purpose : Expansion kinetics of geographic atrophy (GA) can be highly variable between patients, and currently, no predictive model exists. This study evaluates the relationship between the expansion rate of GA, and choriocapillaris flow void (FV) density near the GA margin.

Methods : This prospective study enrolled subjects with GA secondary to non-exudative AMD at the University of California, San Francisco (UCSF) from July 2016 - November 2018. OCT angiography was used to view en face images of the choriocapillaris. Choriocapillaris FV's (Figure 1A) were evaluated using a validated, one-standard deviation thresholding algorithm. Fundus autofluorescence imaging was used to identify margins of GA, and baseline area was subtracted from follow up area to define regions of GA growth (Figure 1B). GA growth rate was measured as the difference in the square root of GA area, divided by the months elapsed between baseline, and follow-up imaging. GA expansion rate was then correlated to the density of FV (%) within a 2-degree band outside the baseline GA margin.

Results : Eight subjects (14 eyes) with GA secondary to non-exudative AMD were imaged once at baseline, and again 7-14 months after baseline. GA expansion rate was positively correlated with increased choriocapillaris FV density at the GA margin (Pearson's correlation coefficient R²= 0.6835, P < 0.01, Figure 2). Mean GA expansion rate was 20.44 µm/month (STD = ± 20.44 µm/month) and mean FV density within a 2-degree band was 18.77% (STD = ± 7.82%).

Conclusions : There was a significant positive correlation between GA expansion rate and choriocapillaris FV density near the GA margin. These results suggest that quantifying regions of choriocapillaris FV may lead to a predictive model for GA growth.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Figure 1: En face illustrations of the choriocapillaris. (a) Baseline GA is outlined in black. The 2-degree band outside of baseline GA is outlined in white. Pink areas represent FV's. (b) The white region represents the difference in the area of GA between baseline GA and follow-up GA.

 

Figure 2: Flow void density (%) within 2-degree band outside of baseline GA margin vs. GA growth rate (Δr/month). Regions with drusen were excluded from analysis.