Automated quantification of choriocapillaris thickness near drusen

Abstract

 

Purpose

 

Choriocapillaris thickness is associated with the progression of drusen in dry age-related macular degeneration. Local quantification of choriocapillaris thickness has so far been difficult. We report an automated method to segment choriocapillaris and to quantify the local/regional choriocapillaris thickness near drusen in dry-AMD using spectral-domain optical coherence tomography (SD-OCT).

 

Methods

 

Sixty-nine patients with dry AMD underwent OCT imaging using Heidelberg Spectralis SD-OCT with enhanced depth imaging. We segmented choriocapillaris and drusen simultaneously using a graph-based method. The boundary of retinal pigment epithelium (l-RPE), Bruch’s membrane (BM) and the transition surface between choriocapillaris and choroidal vasculature (CC-CV) were thus segmented (see Figure 1). Mean and standard deviation (std.) of regional sub-RPE virtual space (sub-RPE-VS) thickness were then calculated for each patient. A drusen was defined as a group of neighboring A-scans where sub-RPE-VS thickness was greater than mean+2*std. Local average choriocapillaris thicknesses was averaged over the drusen region as well as circular regions of 20, 40, to 160 microns near drusen.

 

Results

 

Choriocapillaris is significantly thinner (8.46μm) under the drusen (see Figure 2) and it is thicker (9.19μm) just outside the boundary of the drusen.

 

Conclusions

 

We have developed an automated method to quantify the presence, distribution and size of drusen and measure regional choriocapillaris thickness. Our preliminary results confirm thinner choriocapillaris under drusen that is known from histology studies. Whether the intriguing finding of slightly thickened choriocapillaris just outside of drusen areas can be confirmed is the subject of an ongoing study. Our approach has the potential to better understand the relationships between different structures in the outer retina in dry-AMD.  

 

Figure 1. Automated segmentation of choriocapillaris and drusen (a) Original B-scan; (b) Same B-scan with segmented surfaces.

 

 

Figure 2. Choriocapillaris thickness averaged over the drusen region as well as circular regions of 20, 40, to 160μm near drusen.