Measuring arteriolar-to-venous ratio in retinal photography of patients with hypertension: Development and application of a new semi-automated method

Background: The extent of arteriolar narrowing has been recognized as a major sign of end-organ damage in patients with hypertension, but most methods used for its evaluation are highly dependent on the observer. We describe a new semi-automated method to measuring arteriolar-to-venous (AN) ratio in retinal photography and present its application in the evaluation of patients with hypertension. Methods: In a cross-sectional study, 58 patients with hypertension had retinographies taken and digitized to determine the vessel diameter by direct measurement (micrometric method) or by the new microdensitometric method. Sub-pixel resolution was obtained via cubic spline fitting of the edge of vessel walls. For each pair of adjacent pixels, 10 intermediate points were generated in the perpendicular direction of the wall. Vessel widths were automatically extracted from this synthetic curve, with cut-points defined where the exterior wall position equals the double of mean noise along the slice. Results: The intra- and interobserver kappa statistics for the diagnosis of abnormal AN ratio by the microdensitometric measurements were 0.93 (P <.0001) and 0.85 (P =.0005), respectively. Systolic blood pressure was inversely and significantly associated with the AN ratio measured by the microdensitometric method. Conclusions: The microdensitometric method is reliable, is easy to operate, and captures the expected association between blood pressure and retinal vessels narrowing. Its performance in clinical practice and in the prediction of cardiovascular events should be confirmed in larger databases with retinographies. (c) 2005 American Journal of Hypertension, Ltd.