Abstract
Purpose :
The measurement of pulse wave velocities in retinal veins remains challenging. Here we present a new method to calculate pulse wave velocities (PWVs) in retinal veins using modified photoplethysmographic (PPG) data.
Methods :
A PPG video of the optic disk is acquired spanning three cardiac cycles for a fixed ophthalmodynamometric force (ODF). The video frames are aligned (affine registration) and low pass filtered. A harmonic regression model we have previously described, is fitted to each pixel intensity time series. A binary mask is created for each vein and the centreline pixels are identified. Beginning with the centreline pixel closest to the centre of the optic disc, the distance along the centreline is plotted against the phase of the first harmonic. A least squares line is then fitted in the closed interval defined by the first local maximum and minimum phase values. The velocity is calculated from the reciprocal of the slope of this line.
Results :
Five left eye inferior central retinal veins from five healthy subjects aged between 26 and 33 years old were analysed using this new approach. Videos were acquired at 25 frames per second, containing on average 70 frames. Each frame was a 24-bit RGB image of size 1920x1080 pixels. Velocities were calculated for several intraocular pressures (IOPs) ranging from baseline to 60 mmHg in steps of 5 mmHg. For each pressure the pulse wave velocity was calculated from 100 centreline pixels. In all cases the direction was from the centre to the boundary of the optic disc. The mean speed (velocity magnitude) across all five subjects and pressure steps was 16.45 mm/s (sd = 6.24, range: 3.63 to 52.98).
Conclusions :
This method calculates PWVs from observable retinal venous pulsation. These estimates may serve as a reference for future studies.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.