Quantifying Lateral Pulsation in Retinal Vessels Within the Optic Disc.

Purpose: The retina provides a noninvasive window for imaging vascular pulsation in the optic disc. Pulsation characteristics reflect vascular stiffness, hemodynamics, and ocular pressure dynamics, useful in assessing ocular and systemic cardiovascular health. Whereas axial pulsation can be quantified using modified photoplethysmography (PPG), no reliable method exists for quantifying lateral pulsation. Here, we present a method. Methods: Video of the optic disc is acquired over multiple cardiac cycles. Frames are globally aligned and non-rigidly warped to a common space, then averaged to form a template image from which the vessel of interest is segmented. For each frame, the inverse warp is used to compute sub-pixel vessel wall displacements relative to the template. The method and PPG were applied to a vertically oriented vein in one eye from three healthy subjects. Harmonic regression models were used to compare the vessel wall displacement and diameter pulse waves, with the axial pulse wave from PPG. Results: Where the models fitted well (pseudo-R2 ≥ 75%), the lateral pulse waves were either in phase with the axial pulse wave or showed a small phase delay, with the median phase difference ranging from 4.4% to 9.2% of the cardiac cycle (all P ≤ 0.04). The largest difference between left- and right-wall displacement magnitudes (asymmetric displacement) for each subject were 7.6, 25.2, and 6.33 µm respectively. Conclusions: The results demonstrate the efficacy of the method for quantifying lateral pulsation within the optic disc. Translational Relevance: The proposed method demonstrates proof-of-concept feasibility for quantifying lateral pulsation within the optic disc and lays the groundwork for future biomarker investigation.