Does Retinal Vascular Geometry Vary with Cardiac Cycle?

Abstract

Changes in retinal vascular parameters have been shown to be associated with systemic vascular diseases. In this study, we assessed the physiologic variations in retinal vascular measurements during the cardiac cycle. Fundus images were taken using electrocardiogram-synchronized retinal camera at nine distinct cardiac points from 15 healthy volunteers (135 images). Analyses of retinal vessel geometric measures, including retinal vessel caliber (individual and summary), tortuosity, branching angle, length-diameter ratio (LDR), and optimality deviation, were performed using semiautomated computer software. Repeated-measures ANOVAs were used to obtain the means and to estimate the variation of each cardiac point compared with cardiac point 1. There was a significant variation of the caliber of the individual arteriolar and venular vessels. However, there was no significant variation found for vessel caliber summary, represented by the central retinal arteriolar equivalent (CRAE) and the central retinal venular equivalent (CRVE). There was also no significant variation found for tortuosity and branching angle, and LDR showed none or very little variations at different cardiac points: variations in caliber ranges between 0 and 4.1%, tortuosity 0 and 1.5%, branching angle 0 and 3.5%, and LDR 0 and 2%; all values for variations, P > 0.1; linear trend, P > 0.5; and nonlinear trend, P > 0.8. This study showed that there were minimal variations in the CRAE, CRVE, tortuosity, and branching angle that are clinically used for two-dimensional measures of retinal vascular geometry during cardiac cycles. However, there was significant variation in the caliber of the individual vessels over the cardiac cycle.