Quantification of Pulsatile Changes in Retinal Vessel Calibre to Improve Non-Invasive Cardiovascular Risk Evaluation

Abstract

Background: Large epidemiological studies show that changes in retinal vessel caliber are independently associated with coronary artery disease and stroke. Hence, retinal photography and vessel measurement have excellent potential for the non-invasive risk prediction of these important pathological conditions. This study aims to improve the precision of cardiovascular risk evaluation using retinal photography by developing an ECG gated method for the study of the pulsatility in retinal vessels. Methods: High-resolution red-free digital photographs were taken throughout the cardiac cycle in ten healthy volunteers using an ECG gating method developed by our biomedical engineering department. Vessel diameters were measured using a semi-automated computer analysis program. The ECG gating methodology was then validated in ten patients with known or suspected coronary disease and compared to un-gated photography. Results: We were able to detect a statistically significant difference (p < 0.001) between trough and peak measurements with mean changes from trough to peak being 3%. Retinal arteriolar pulsatility corresponded well with pulse waves from the temporal and carotid arteries, with a trough occurring in systole, a peak in early diastole and a slow decline in late diastole. Minimum variability between gated photographs occurred in systole with maximum variability occurring in early diastole. ECG gating resulted in a significant (p<0.001) reduction in variability with variances of 1.98µm with and 4.00µm without ECG-gating. Conclusion: ECG gated retinal photography enables the detection of small changes in retinal vessel diameter throughout the cardiac cycle. The retinal arterioles demonstrate similar pulsatility to other peripheral arteries with a change in diameter of 3%. ECG gating significantly reduces variability in retinal arteriolar diameter measurements.