Absolute retinal blood flowmeter using a laser Doppler velocimeter combined with adaptive optics

Abstract

Significance: The development of a technique allowing for non-invasive measurement of retinal blood flow (RBF) in humans is needed to understand many retinal vascular diseases (pathophysiology) and evaluate treatment with potential improvement of blood flow. Aim: We developed and validated an absolute laser Doppler velocimeter (LDV) based on an adaptive optical fundus camera that provides simultaneously high-definition images of the fundus vessels and absolute maximal red blood cells (RBCs) velocity to calculate the absolute RBF. Approach: This new absolute LDV is combined with the adaptive optics (AO) fundus camera (rtx1, Imagine Eyes © , Orsay, France) outside its optical wavefront correction path. A 4-s recording includes 40 images, each synchronized with two Doppler shift power spectra. Image analysis provides a vessel diameter close to the probing beam, and the velocity of the RBCs in the vessels are extracted from the Doppler spectral analysis. A combination of these values gives an average of the absolute RBF. Results: An in vitro experiment consisting of latex microspheres flowing in water through a glass capillary to simulate a blood vessel and in vivo measurements on six healthy humans was done to assess the device. In the in vitro experiment, the calculated flow varied between 1.75 and 25.9 μL∕ min and was highly correlated (r 2 ¼ 0.995) with the flow imposed by a syringe pump. In the in vivo experiment, the error between the flow in the parent vessel and the sum of the flow in the daughter vessels was between −11% and 36% (mean AE sd, 5.7 AE 18.5%). RBF in the main temporal retinal veins of healthy subjects varied between 0.9 and 13.2 μL∕ min. Conclusions: The AO LDV prototype allows for the real-time measurement of absolute RBF derived from the retinal vessel diameter and the maximum RBCs velocity in that vessel.

The influence of vortices on hemodynamics in blood vessels

“…Despite the potential drawbacks of vortices in blood vessels, they also have potential benefits for diagnostic and therapeutic purposes. For example, the presence of vortices can indicate the presence of obstructions or changes in vessel diameter [4,5], which can be useful for diagnosing cardiovascular diseases. Additionally, vortices can also be used as a therapeutic tool to improve blood flow and prevent the formation of stenosis or aneurysms.…”

“…HWA has a good signal-to-noise ratio, suitable for studying low-intensity turbulence and spectra. Another LDV suitable for high-intensity fluctuations and accurate timing [7,8]. However, neither technique offers the ability to obtain spatial derivatives, visualize flow, or provide the spatial correlation capabilities that PIV offers.…”

Current State of Knowledge in Ocular Blood Flow in Glaucoma: A Narrative Review

“…Clinicians and researchers can get a better understanding of the hemodynamics of the retinal circulation using this BF assessment as it can also provide information on the resistance and pulsatility indices of the retinal blood vessels. 43 This technique is helpful in studying various retinal vascular conditions such as diabetic retinopathy, retinal vein occlusion, and hypertensive retinopathy. 44 …”

“…understanding of the hemodynamics of the retinal circulation using this BF assessment as it can also provide information on the resistance and pulsatility indices of the retinal blood vessels. 43 This technique is helpful in studying various retinal vascular conditions such as diabetic retinopathy, retinal vein occlusion, and hypertensive retinopathy. 44 The main setback of this technique is that it may be staggered by eye movements and other displacements, media opacities can give rise to blurred images and thus cannot measure circulation in the optic nerve head (ONH).…”