Abstract
Purpose :
We aimed to validate a new prototype (LDVao) which allows high resolution retinal vessel diameter measurement and real-time calculation of retinal blood velocity and blood flow.
Methods :
A bidirectional laser Doppler velocimeter was coupled to an adaptive optics fundus camera (rtx1, Imagine Eyes®). A 4° x 4° fundus area was illuminated at 840nm by a temporally low coherent light emitting diode flashed flood source, with a resolution of 250 line pairs per millimeter. The in vitro experiment was performed with a microsphere solution containing a capillary simulating a blood vessel. A calibrated syringe pump with controlled velocity regulated the velocity of the solution inside the capillary. For the in vivo experiment the blood flow was measured in first order temporal retinal arteries and veins in healthy subjects. Each measurement was acquired in 4 s (10 images and Doppler spectrum per second)
Results :
The Doppler measurements of the flow rate in a 447µm glass capillary varied between 0.59 µL/s and 7.02 µl/s with a correlation factor of 0.99 with the controlled flow. In healthy humans, the measurement of the diameter as well as the calculation of the blood velocity and blood flow was performed in 15 temporal retinal veins (diameters: 142-168 µm; flow rate: 1.8±0.6 µl/s) and 15 temporal arteries (diameters: 104-118 µm; flow rate: 2.7±0.9 µl/s). For a laminar flow, the velocities distribution within a vessel was constant up to the maximal velocity. This distribution was always observed in the Doppler spectrum in vitro. In vivo, this distribution was only observed when the laser beam was perfectly aligned with the retinal blood vessel.
Conclusions :
Velocity values measured in vitro covered a range wider than the velocity expected in vivo. In vitro Doppler measurements were highly correlated and similar to the theoretical flow values imposed in the capillary. These results consistent with known velocities within the retina showed that this new prototype LDVao allows real-time absolute retinal blood flow measurement using high resolution evaluation of the inner vascular diameter and red blood cell velocity.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.