Hypertension-associated changes in retinal blood vessel walls measured in vivo with polarization-sensitive optical coherence tomography

Blood vessel walls are made of organized fibrous tissue with intrinsic birefringence. Even in its very early stages, hypertension can change the structure of a blood vessel wall. In this paper, we demonstrated that this structural change associated with hypertension can be quantitatively measured non-invasively in the human retina using polarization-sensitive optical coherence tomography (PS-OCT). Measurements were performed with a relatively low-cost PS-OCT instrument in less than a minute per eye. Organizational loss in vessel wall tissue was quantified in hypertensive patients and compared to data obtained from age-matched healthy subjects. Our PS-OCT measurements showed that the vessel wall tissue in patients with hypertension is thicker, and exhibited lower birefringence, presumably due to a loss of tissue organization. The blood vessel wall birefringence index (BBI) is a newly introduced metric that combines vessel wall birefringence (decreases with hypertension) and thickness (increases with hypertension) into a single numerical value. Its purpose is to easily differentiate between the blood vessel walls of hypertensives and those of healthy subjects. Accurately determining the thickness of the blood vessel wall relies on access to polarization-sensitive data: a linear increase in retardation in the vessel wall with depth and stable retardation values below the vessel wall to determine the lower edge of the vessel wall. Based on receiver operating characteristic (ROC) curves, BBI showed 99 % sensitivity and 100 % specificity when discriminating normotensive (N = 11) and hypertensive (N = 11) subjects.