Influence of Axial Length on Parafoveal and Peripapillary Metrics from Swept Source Optical Coherence Tomography Angiography

Abstract

Purpose: To assess the effect of axial length (AL) on the quantification of superficial vessel density of both macular and disc region using swept source optical coherence tomography angiography (SSOCTA). Methods: This is a cross-sectional clinical study. Seventy-five eyes from 75 Chinese healthy participants (56 females) with a mean age of 26.6 ± 6.8 (range 19-50) years were included in this study. All eyes were imaged with SSOCTA, using a 3 × 3mm scan pattern centered on the macular and optic disc, respectively, and the superficial layer was used for evaluation. The image size was corrected with AL using Bennett formula. Outcome measurements included perfusion density (PD), vessel length density (VLD) in parafoveal and disc regions, averaged peripapillary large vessel diameter and area of foveal avascular zone (FAZ). Image processing and measurements was performed using Image J software. Multivariate regression analysis adjusting for age and signal strength was used to assess the influence of AL on the metrics. Results: AL was the only predictive factor for parafoveal PD (β = -0.273, P = .047) and VLD (β = -0.396, P = .003). There was no correlation between AL and area of FAZ, large vessel diameter, or the vessel density on any location in disc region. Age was the only predictor for PD (β = -0.287, P = .024) and VLD (β = -0.289, P = .023) on optic nerve head. Conclusions: AL was negatively correlated with superficial parafoveal microvasculature, but not correlated with peripapillary capillaries, suggesting that the inner retina stretches more in the distal end of the disc with increased AL.

Keywords: Swept source OCTA (SSOCTA); axial length (AL); macular; perfusion density (PD); peripapillary; vessel length density (VLD).