ARTICLE Mautuit_MICROVASCULARRESEARCH_2024/IDIAP Absolute retinal blood flow in healthy eyes and in eyes with retinal vein occlusion Mautuit, Thibaud Cunnac, Pierre Truffer, Frédéric Anjos, André Dufrane, Rebecca Maître, Gilbert Geiser, Martial Chiquet, Christophe EXTERNAL http://publications.idiap.ch/attachments/papers/2024/Mautuit_MICROVASCULARRESEARCH_2024.pdf PUBLIC Microvascular Research 152 0026-2862 2024 10.1016/j.mvr.2023.104648 doi Purpose: To measure non-invasively retinal venous blood flow (RBF) in healthy subjects and patients with retinal venous occlusion (RVO). Methods: The prototype named AO-LDV (Adaptive Optics Laser Doppler Velocimeter), which combines a new absolute laser Doppler velocimeter with an adaptive optics fundus camera (rtx1, Imagine Eyes®, Orsay, France), was studied for the measurement of absolute RBF as a function of retinal vessel diameters and simultaneous measurement of red blood cell velocity. RBF was measured in healthy subjects (n = 15) and patients with retinal venous occlusion (RVO, n = 6). We also evaluated two softwares for the measurement of retinal vessel diameters: software 1 (automatic vessel detection, profile analysis) and software 2 (based on the use of deep neural networks for semantic segmentation of vessels, using a M2u-Net architecture). Results: Software 2 provided a higher rate of automatic retinal vessel measurement (99.5 % of 12,320 AO images) than software 1 (64.9 %) and wider measurements (75.5 ± 15.7 μm vs 70.9 ± 19.8 μm, p smaller than 0.001). For healthy subjects (n = 15), all the retinal veins in one eye were measured to obtain the total RBF. In healthy subjects, the total RBF was 37.8 ± 6.8 μl/min. There was a significant linear correlation between retinal vessel diameter and maximal velocity (slope = 0.1016; p smaller than 0.001; r2 = 0.8597) and a significant power curve correlation between retinal vessel diameter and blood flow (3.63 × 10−5 × D2.54; p smaller than 0.001; r2 = 0.7287). No significant relationship was found between total RBF and systolic and diastolic blood pressure, ocular perfusion pressure, heart rate, or hematocrit. For RVO patients (n = 6), a significant decrease in RBF was noted in occluded veins (3.51 ± 2.25 μl/min) compared with the contralateral healthy eye (11.07 ± 4.53 μl/min). For occluded vessels, the slope between diameter and velocity was 0.0195 (p smaller than 0.001; r2 = 0.6068) and the relation between diameter and flow was Q = 9.91 × 10−6 × D2.41 (p smaller than 0.01; r2 = 0.2526). Conclusion: This AO-LDV prototype offers new opportunity to study RBF in humans and to evaluate treatment in retinal vein diseases.