Effect of age and signal strength index on retinal and choriocapillaris vessel density measured with optical coherence tomography angiography

Abstract

Purpose : This study aims to determine the relationship of age and signal strength index (SSI) with retinal vessel density and choriocapillaris (CC) vessel density derived with optical coherence tomography angiography (OCTA).

Methods : Study participants with normal ocular exams were enrolled in an observational cross-sectional study. Two 3×3-mm OCTA scans were acquired with the spectral domain OCT (Avanti, Optovue, Inc) and exported for custom processing. Retinal vessel density was calculated from en face OCT angiograms between the internal limiting membrane and the outer plexiform layer, inclusively. CC vessel density was calculated from 7 µm to 21 µm deep to Bruch’s membrane. Vessel density, defined as percentage area occupied by blood vessels, was calculated using an automated thresholding algorithm. Projection artifact from large retinal vessels was masked from CC OCT angiograms. Using SPSS, we performed univariate and multivariate linear regression to examine the dependence of vessel density on age and SSI.

Results : Forty participants were enrolled and two were excluded due to poor image quality. After randomly selecting one eye from each participant, we analyzed 38 eyes of 38 participants (16 males) with a mean age of 63.6 ± 11.5 years (range 40-85). In univariate analysis (Table 1), retinal vessel density, but not CC vessel density, was significantly correlated with age and SSI. SSI showed significant reduction with age. After accounting for the effect of SSI in multivariate analysis (Table 2), age no longer had a significant effect on retinal vessel density. Vessel density measurements had good within-visit repeatability (pooled standard deviation) of 4.72% and 1.10% for retinal and CC vessel density, respectively.

Conclusions : The apparent relationship between retinal vessel density and age was not due to vascular aging changes but was an artifact due to lower OCT signal strength in older participants. The influence of SSI should be accounted for during quantitative analysis of retinal vessel density using OCTA. CC vessel density was not associated with age or SSI.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.