Retinal capillary and choriocapillaris assessment using Beam Expander module

Abstract

Purpose : To assess the effect of an increase in the lateral resolution of the OCT beam, on the retinal and choriocapillaris optical coherence tomography angiography (OCTA) en face images .

Methods : Prototype software was used on the PLEX® Elite 9000 Swept-Source OCT instrument (ZEISS, Dublin, CA) in combination with the beam expander (BE) module in the OCT path, which produces a wider beam at the pupil plane. This configuration provides a 17 um optical resolution at the retina compared to the standard 24 um resolution.
This retrospective study involved 23 healthy subjects imaged with 3 × 3 mm and 2.25 x 2.25 mm OCTA scans repeated at least 3 times for each subject. The 3x3 mm and 2.25x2.25 mm scans were acquired without and with the BE respectively.
The angiograms were aligned and cropped to keep the part common to both images. Two graders analyzed the images. Perfusion density (PD), vessel density (VD), and foveal avascular zone (FAZ) measurements were also compared.

Results : Qualitative analysis of retinal angiograms acquired with the BE showed significantly better vessel sharpness (p=0.0005), better peripheral image quality (p=0.0001) and a decrease in segmentation errors (p=0.04) compared to scans acquired without the BE.
Mean VD was significantly higher for BE angiograms compared to classic angiograms (25.86 ± 1.12 mm^-1 and 21.5 ± 1.13 mm^-1, respectively, p<0.0001), whereas mean PD was not significantly different between the 2 groups.
Mean FAZ circularity was found to be significantly lower in BE angiograms (0.65 ± 0.14 mm^-1 and 0.69 ± 0.08, p=0.0067) whereas mean FAZ area was not significantly different between the 2 groups.
Repeatability of VD, PD and FAZ measurements were higher for BE angiograms (ICC : 0.662 ; 0.536 and 0.874 with BE, vs 0.439; 0.435 and 0.804 without BE).
Choriocapillaris image quality was found to be significantly superior with BE, and flow deficits were more visible in all BE scans compared to “classic” scans.

Conclusions : An increase in lateral resolution of the OCT beam resulted in higher quality of retinal and choriocapillaris OCTA images. Improved vessel sharpness and higher mean VD were significant in the scans acquired with the BE. The improvement was also very significant for choriocapillaris definition, particularly in the visualization of flow deficits

This is a 2021 ARVO Annual Meeting abstract.