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Editors Selection IGR 13-2

Blood Flow: Volumetric blood flow in absolute units

Comment by Alon Harris on:

23874 Volumetric blood flow measurement in the ophthalmic artery using colour Doppler, Katamay R; Fleischlin C; Gugleta K et al., Klinische Monatsblätter für Augenheilkunde, 2009; 226: 249-253

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Volumetric blood flow measurement in the ophthalmic artery using color Doppler
Progress in measuring the ocular circulation is essential for further understanding the pathophysiology of various ophthalmic diseases including glaucomatous optic neuropathy. Among the various imaging technologies currently available, each imaging device presents interesting information regarding ocular hemodynamics, but every device has inherent limitations. In the present study, Katamay et al. (707) present a method for the measurement of volumetric blood flow in absolute units within the ophthalmic artery. Utilizing a Philips EnVisor HD ultrasound unit with a 12-3 MHz linear transducer, ophthalmic artery flow was measured in the 8 healthy young subjects. The authors built a custom-made transducer holder to allow reproducible positioning in 3 axes as well as in rotation angle. Blood vessel diameter and blood flow velocity were calculated and combined using various assumptions and relationships. Average blood flow in the ophthalmic artery in all measurements was 39.7 mL/min. The short-term (5 measurements on day 1) intraindividual coefficient of variation was 24.1 ± 9.2%, the long-term (5 days once daily) coefficient 32.0 ± 13.8%. Interindividual coefficient of variation was 32.8%. The authors suggest that their method allows volumetric blood flow measurements in the ophthalmic artery with somewhat limited reproducibility. This study follows previous research by Orge et al.1 which reported the first technique for non-invasive measurements of volumetric flow in the ophthalmic artery.

Minimizing observer error by accounting for reproducible color Doppler probe placement and angle may indeed benefit reproducibility of measurements. The assumption of diameter based upon visual interpretation of color Doppler images is, however, uncertain. Utilizing these values in combination with various transformational calculations into absolute units of flow should be verified to a known standard, perhaps in a phantom flow model. A further limitation to the study was the inclusion of only 8 healthy subjects. Katamay et al. attempt to improve ocular hemodynamic assessment techniques are important and should be encouraged in all capacities of ocular blood flow research.

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