A novel electrocardiogram-synchronized laser Doppler holography system for cardiac cycle-resolved retinal...

The retinal microvasculature is one of the few sites where the microcirculation can be directly and non-invasively visualized in vivo, offering a unique window into ocular disease and systemic health. In this study we developed and validated a novel imaging platform integrating a custom-built one-lead electrocardiogram (ECG) with laser Doppler holography (LDH), a high-speed imaging technique that captures Doppler-induced phase shifts, for real-time cardiac cycle-resolved assessment of retinal hemodynamics. Twenty-five healthy adults were imaged (five images per eye), with 563 cardiac cycles meeting analysis quality criteria. Internal system latency combined with synchronization offset amounted to less than 5 ms. LDH-derived beat-to-beat intervals closely tracked ECG R-R intervals, with small mean differences (~ 3 ms), demonstrating excellent temporal stability without measurable drift. ECG-retina latencies, defined as time from the ECG R-peak to LDH peak systolic velocity (R-PSV), maximal systolic upslope (R-MaxSlope), and 50% PSV amplitude (R-PSV½), were measured. R-PSV½ mean ± SD was 128 ± 18 ms and showed the highest repeatability (ICC = 0.78, median CV = 4.8%). ECG-retina latencies were moderately associated with age and heart rate, in exploratory analyses. This integrated ECG-LDH platform provides repeatable, synchronized, high-speed, cardiac-resolved retinal hemodynamic measurements and establishes a quantitative framework for studying the eye-heart relationship.