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Étude morphométrique des artérioles rétiniennes chez l’homme par imagerie a haute résolution

Abstract : Small arteries (i.e. diameter less than 150μm), so-called resistive arteries, are essential for regulating the distribution of blood flow. These vessels are modified during many conditions, including arterial hypertension which causes a thickening of their wall. Until recently, direct observation of retinal vessels was not possible in humans. Following the discovery by our team of the possibility of visualizing the wall of the retinal vessels in humans using an imaging technology using adaptive optics (OA), we studied normal and pathological human retinal vascular morphometry. For this, original clinical protocols have been implemented, in collaboration with computer scientists, ophthalmologists and cardiologists. After contributing to the development of image segmentation software to extract quantitative data on retinal vascular morphometry, we conducted prospective, observational, cross-sectional and longitudinal clinical studies. This work enabled us to validate a methodology for measuring parameters related to the microvascular structure, and to study its variations during hypertension and during focal pathologies (arteriovenous nicking, focal arteriolar narrowing). We were able to demonstrate that the variability of the retinal artery wall-to-lumen ratio (WLR) was 43% correlated with the blood pressure measured in consultation and to a lesser extent at age. This remodeling is eutrophic (i.e. without increasing the amount of the parietal material). The observation of focal arterial narrowing revealed a decrease in the internal diameter without parietal thickening and in some cases a disappearance of the focal narrowing, which suggests that these arterial narrowing are due to localized vasoconstriction. Finally, we have demonstrated that venous abnormalities occur near the arteries without direct contact with them, suggesting the existence of an indirect effect of the proximity between artery and veins on venous morphology. In diabetics, the team of Xavier Girerd with our contribution has demonstrated the existence of hypertrophic remodeling (increase in the amount of parietal material with reduction of light and parietal thickening). In patients with acute cerebral infarction, we found no correlation between the WLR and the Fazekas score, reflecting the degree of leukoaraiosis; the WLR itself is not significantly modified relative to a control population. We also studied the dynamics of retinal vasomotricity. Through various vasoconstrictor stimuli (oxygen, cold) and vasodilators (intermittent light stimulation, hypotensive treatment), we have documented the corresponding changes in caliber of small arteries and veins. Intermittent light stimulation appears to be the most promising method because of its simplicity and acceptability. In conclusion, through this work, we explored new methods of in vivo study of human retinal circulation. A broad field of clinical studies is opening up in the field of phenotyping microcirculation. Future work may be directed towards a better prediction of the risk of organic lesion, towards the follow-up of the hypotensive treatment and towards the role of the modifications induced by the diabetes in the occurrence of the diabetic retinopathy.
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Edouard Koch. Étude morphométrique des artérioles rétiniennes chez l’homme par imagerie a haute résolution. Neurosciences [q-bio.NC]. Sorbonne Université, 2018. Français. ⟨NNT : 2018SORUS418⟩. ⟨tel-02924872⟩

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