Arterial stiffness and pulse wave velocity quantification in bovine retinal arteries

Purpose : Recent published studies have reported attempts to non-invasively quantify retinal pulse wave velocity (rPWV) as a measure of retinal artery stiffness. However, the reported values in those studies differ by a magnitude of order (mm/s and cm/s). Which is correct is unknown as the true stiffness of the vessels has never been measured. The aim of this study was to measure the elastic modulus (E) and geometry of retinal arteries and calculate rPWV using the Moens-Korteweg equation. By measuring material stiffness and vessel geometry, the order of magnitude of rPWV can be determined. Methods : Bovine eyes (n=7) were stored in 0.9% saline and kept in 4oC after animal euthanasia and tensile testing was done within 24 to 72 hours. One segment of the primary branch of retinal artery adjacent to the optic disc in each eye was isolated and tensile tested using a wire myograph. An immediate distal artery segment was stored in formalin overnight and mounted and stained (Hematoxylin and Eosin) for geometry (wall thickness, diameter) measurements by microscopy. Results : The average luminal diameter and wall thickness were 130 µm and 7.75 µm respectively and were used across all samples for rPWV calculation. Stress-strain curves were curvilinear, typical of arteries. At a transmural pressure of 100 mmHg, E was 1509±746 kPa and the resultant rPWV was 8.9±2.7 m/s. Conclusions : The obtained rPWV is in the same range as PWV in large arteries and also the latest reported rPWV in mouse retina (more than 1 m/s) using swept-source optical coherence tomography. From a physiological point of view, near-constant PWV throughout the vascular network is rational. This study gives a reference value for PWV in retinal arteries and provides confirmation for non-invasive rPWV measurement, opening new avenues for using rPWV as a marker of cardiovascular related pathogenesis.