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Jonathan Benesty, Edouard Koch, David Rosenbaum, Xavier Girerd, José Sahel, Florence Rossant, Isabelle Bloch, Michel Paques; High resolution imaging of retinal vascular network geometry. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5296.
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© ARVO (1962-2015); The Authors (2016-present)
An energetically optimal vascular network should theoretically respect some physical principles among which the cubic mathematical relationship between parent and daughter vessels at bifurcations (Murray’s law). Deviations from this optimal geometry have been reported in several vascular diseases. The availability of high resolution imaging of vessels offers the opportunity to reevaluate these results. Here, following our initial evaluation of adaptive optics (AO) retinal vascular imaging (Koch et coll. 2014), we mathematically analyzed arterial and venous bifurcations to calculate more precisely the junction exponent and to evaluate the effect of cardiovascular risk factors.
Flood-illumination AO imaging was done in 93 arterial and 25 venous bifurcations of 21 controls and 65 patients (mean age 45.7 years ±15.2; M/F 44/49) with various cardiovascular risk factors (hypercholesterolemia, hypertension, diabetes, smoking). A semi-automated procedure was used to measure vascular diameters and angles.
In control arteries, the mean value of the arterial junction exponent (theoretically equal to 3) was 2.80 (±0.44). The linear regression for measured vs predicted parent arterial diameter was 0.993 with a coefficient of determination R2=0.942. Mean arterial bifurcation angle measured was 85.05° (±11.7°), which was significantly different from the mean optimal angle 71.7°(±13.9°) (p<0.01). In the cardiovascular risk group, the arterial junction exponent was significantly higher than controls (3.24±1.4 versus 2.8±0.44; p=0.02) but not the venous junction exponent (2.47 ±0.45 versus 2.42 ±0.46; p=0.8). The junction exponent in the diabetic group (n=9) was 3.9 (±2.5), no difference was found with the control group (p=0.25) but it might be a consequence of the small number of diabetic patients.
In arterial bifurcations of normal eyes, the junction exponent is not significantly different from 3, further confirming Murray's law as a general principle for small arteries but not veins. Patients with cardiovascular risk factors have a higher arterial junction exponent, suggesting an alteration of flow distribution. AO imaging of arterial bifurcations may therefore provide a novel biomarker of the general vascular state. Further studies are needed to understand the anatomical, functional and clinical significance of this finding.
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