Evidence for the Existence of Two Opposing Pulse Waves in Retinal Vein Segments Within the Optic Disc.

Purpose: Pulse wave velocity (PWV) is used to assess vascular disease. We recently introduced a non-invasive technique for measuring retinal PWVs and presented evidence of venous pulse wave propagation opposite blood flow in the central optic disc close to maximum pulsation. The purpose of this study was to characterize venous pulse wave propagation more peripherally in the optic disc, where little is currently known about its dynamics. Methods: We measured PWVs in optic disc veins in six healthy eyes at varying intraocular pressures (57 measurements in total). Our technique involves acquiring video of the retina over three cardiac cycles, fitting a harmonic regression model to the wave-like pattern of green channel intensities at each point along the vessel centerline, and using the differences in wave timing (phase) to calculate PWVs. Results: The mean age was 42.3 ± 18.6 years, and the mean intraocular pressure was 33.2 ± 13.3 mm Hg. All distance-phase plots showed a linear down trend followed by a linear up trend, suggesting a PWV retrograde to blood flow before the turning point and anterograde thereafter. The turning point was located a mean distance of 0.14 ± 0.12 mm from the point of maximum pulse amplitude. The distances of the turning point and maximum pulse amplitude from the optic disc center were positively associated (P = 0.013). Conclusions: These results suggest that two opposing pulse waves travel along retinal vein segments within the optic disc, raising the possibility that at least two distinct pulse wave generators exist either side of the lamina cribrosa.