The Effect of Scan Size and Device on OCT-A Retinal Vasculature Metrics

Abstract

Purpose : To investigate the effect of scan size and device on quantitative metrics used to describe optical coherence tomography angiography (OCT-A) images of the retinal vasculature.

Methods : 19 eyes of 19 subjects without ocular pathology were imaged using the Optovue AngioVue system at three scan sizes (3mm, 6mm HD, 8mm), generating 57 total images that were aligned, scaled, and cropped to a common area for each subject. 20 eyes of 20 subjects without ocular pathology were imaged using the AngioVue and Zeiss AngioPlex systems, generating 40 total images that were aligned and cropped to a common area for each subject. The foveal avascular zone (FAZ) was segmented manually to estimate FAZ area and acircularity, and parafoveal intercapillary area (PICA) and vessel morphology metrics were computed as previously described.^{1, 2, 3}

Results : There were no significant differences in FAZ metrics imaged using the AngioVue device when compared across scan size. Vessel density was higher in 6x6mmHD scans (repeated one-way ANOVA, p < 0.0001). Average PICA increased as scan size increased (repeated one-way ANOVA, p < 0.0001), while total PICA was only larger in 3x3mm when compared to 6x6mmHD scans (repeated one-way ANOVA, p = 0.22). The 8x8mm scans had fewer total endpoints than the 3x3mm and 6x6mmHD scans, whereas maximum branch length and average single branch length increased as scan size increased (repeated one-way ANOVA, p < 0.0001). When using different devices, there was a small but significant increase in FAZ area (paired t-test, p = 0.024), average PICA (paired t-test, p = 0.016) and total PICA (paired t-test, p < 0.0001) in the AngioVue when compared to the AngioPlex, but decreased FAZ acircularity (paired t-test, p = 0.001) and fewer total endpoints (paired t-test, p = 0.018). No other metrics significantly varied when compared across scan device. All image size and device measurements are shown in Tables 1 and 2, respectively.

Conclusions : While scan size appears to have minimal impact on FAZ metrics, it can affect PICA and vessel morphology metrics, which are more dependent on image resolution. Conversely, scan device appears to have a robust effect on FAZ metrics. These differences indicate that OCT-A data are not interchangeable across the acquisition variables examined here.
¹PMID: 28616362
²PMID: 30009090
³PMID: 28068370

This is a 2020 ARVO Annual Meeting abstract.