Retinal Blood Flow Evaluation

Abstract

Much of our basic knowledge of retinal blood flow regulation is based on data obtained from animal experiments through the use of invasive techniques. However, during the last decades, major developments in the field of optics and lasers have led to a variety of noninvasive techniques, which have been applied to the human eye for the investigation of retinal hemodynamics, and more specifically the regulation of retinal blood flow in response to a number of physiological and pharmacological stimuli. The Retinal Vessel Analyzer has markedly simplified the measurement of the diameter of retinal vessels, as well as the change in this diameter evoked by various physiological stimuli (dynamic measurements). Bidirectional laser Doppler velocimetry allows the measurement of absolute red blood cell centerline velocity, which, when combined with the diameter allows the calculation of retinal blood flow in the main retinal vessels. Laser Doppler flowmetry and laser speckle flowgraphy are techniques that measure the velocities of blood in discrete areas of the retinal tissue microcirculation. Adding a scanning capability, a spatial map of velocities across the retinal tissue is obtained. The blue-field simulation technique allows the quantification of the velocity, number and velocity pulsatility of leukocytes moving in the retinal capillaries of the macular region. With color Doppler imaging, the peak systolic and end-diastolic values of blood velocity in the ophthalmic and central retinal artery are measured, from which a resistivity index is obtained. These techniques may help better understand the role of altered retinal blood flow and its regulation in the pathogenesis of retinal diseases of vascular origin.

Measurement of retinal blood flow in the rat by combining Doppler Fourier-domain optical coherence tomography with fundus imaging

“…6,19,[28][29][30] Doppler OCT is a promising approach for measuring retinal blood flow. If absolute blood flow is to be measured, the angle ambiguity of the Doppler techniques has to be resolved.…”

“…11,12,15 Recently, several systems were realized aiming toward the quantification of retinal blood flow using Doppler OCT in humans. [16][17][18][19][20] We set out to develop a novel system that is capable of measuring changes in retinal blood flow in the rat. The system uses the combination of Fourier-domain Doppler OCT for the extraction of retinal blood velocities and a fundus camerabased optical part of the system for the measurement of retinal vessel diameters.…”

The clinical implications of recent studies on the structure and function of the retinal microvasculature in diabetes

“…Retinal blood flow can be estimated non-invasively by a bidirectional laser Doppler velocimetry system, which measures the absolute values of the red blood cells flowing in the centre line of the main retinal vessels. Laser Doppler flowmetry and laser speckle flowgraphy can also be used to quantify retinal blood flow noninvasively to evaluate the retinal haemodynamics [81,82].…”

Evaluating anesthetic protocols for functional blood flow imaging in the rat eye

“…This interest is attributable to the importance of ocular blood flow as a parameter in studies of ocular pathophysiology and its potential to serve as an early marker of a variety of ocular diseases, including age-related macular degeneration, diabetic retinopathy, and glaucoma. The importance of ocular blood flow has driven the development of multiple measurement technologies including retinal/dynamic vessel analysis, 1 microsphere methods, [2][3][4] laser Doppler-based velocimetry [5][6][7][8] and flowmetry, [9][10][11] laser speckle imaging, [11][12][13] magnetic resonance imaging (MRI), [14][15][16] color Doppler ultrasound imaging, [17][18][19] and optical coherence tomography (OCT). [20][21][22][23][24][25][26][27][28][29][30][31] En face Doppler OCT, the modality used in this study, is a noninvasive, OCT-based technique that measures the Doppler velocities in the en face plane.…”