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Editors Selection IGR 7-2

Clinical Examination Methods: Novel non-invasive laser Doppler flowmeter

Comment by Alon Harris on:

45637 A novel, microscope based, non-invasive laser Doppler flowmeter for choroidal blood flow assessment, Strohmaier C; Werkmeister RM; Bogner B et al., Experimental Eye Research, 2011; 92: 545-551

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Research dedicated to the accurate assessment of ocular blood flow continues to show promise at helping identify the physiology and mechanisms behind many ocular pathologies. One impediment to the advancement of understanding risk factors for glaucoma and other eye diseases in terms of the ocular circulation is the lack of a gold standard methodology. No single imaging device is capable of assessing all of the relevant ocular vascular beds and each imaging device has specific benefits and limitations. Strohmaier et al. (739) present data on a novel, microscope based, non-invasive laser Doppler flowmeter for choroidal blood flow assessment. The authors data suggest the NI-LDF measurements correlate linearly to intraluminal flow rates in a perfused tubing model (r = 0.99, p < 0.05) and are in strong agreement with the Perimed PF4000, a fiber optic based laser Doppler flowmeter. The authors should be commended for their efforts to validate this technology before implimenting it in clinical trials. Too often researchers fail to adress methodological limitations or perform validation studies on vascular imaging technologies. Another strength of the current study is the use of both a silastic tubing model (i.d. 0.3 mm) at different flow rates (range 0.4-3 ml/h) and a rabbit model providing a more robust pilot analysis. Several areas of concern should also be noted however in the author's conclusions. First, the Peimed system is mostly intended for skin flow measurements so differences in penetration depth from different probe wavelengths of each system are uncertain. Other areas of possible limitation include different sample areas of each method, spectral Doppler broadening resulting in a signal that integrates Doppler shifts from capillaries as well as larger vessels, duration of measurement time and specificity of signal location. As it relates to glaucoma, the measurement of choroid blood flow as specifically assessed with this technology is unknown. The rabbit eye also has different physiology than human eyes so comparative data from a healthy human and glaucoma population is required. At this stage, the reviewer recommends a comprehensive approach evaluating multiple vascular beds relevant to glaucoma including retinal, choroidal, retrobulbar and optic nerve head blood flow.

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