Pedro BARAÇAL DE MECÊ

Résumé: We measured neurovascular coupling (NVC) in the living human retina using an Adaptive Optics Rolling Slit Ophthalmoscope, achieving sub-micrometer spatial precision and 10 ms temporal resolution. Flicker stimulation induced a significant arterial dilation (~5%) with a rapid, triphasic response, distinct from baseline vascular fluctuations. This approach enables high-resolution, stimulus-specific assessment of retinal NVC and may support early detection of neurovascular dysfunction in retinal diseases Purpose: Neurovascular coupling (NVC) - the process by which blood vessels respond to neuronal activity - plays a critical role in maintaining visual processing and metabolic homeostasis in the retina. Its disruptions has been linked to early stages of neurodegenerative and eye diseases, such as glaucoma and diabetic retinopathy [1-3]. Despite its importance, directly and precise measurement of NVC in the human retina has remained a major challenge due to the limitations of current in vivo imaging modalities. Most techniques either lack the spatial resolution or contrast to visualize fine vascular structures and track micrometer changes of vessel diameter or the temporal resolution to track rapid neurovascular dynamics and separate the effect of NVC from spontaneous vascular changes due to the cardiac cycle or vasomotion. Here, we use our Adaptive Optics Rolling Slit Ophthalmoscope (AO-RSO) [4] to measure retinal NVC in the living human eye with sub-micrometer precision and 10 ms temporal resolution. This is enabled by AO-RSO’s ability to generate high-speed, phase-contrast images across a wide field of view (FOV). Methods: The AO-RSO synchronizes line-scanning illumination with the rolling shutter of a high-speed 2D camera [4]. By introducing an offset between the illumination and the shutter, phase-contrast images—similar to those in off-axis AO-SLO—are generated [5,6]. Unlike AO-SLO, AO-RSO employs a 2D sensor, allowing for higher frame rates (up to 100 Hz) and a broader field of view (4.5° × 4.5°). Additionally, its 1D scanning design minimizes motion-induced distortions [7]. Images were acquired in 8 subjects. Each session included a 40s baseline recording without flicker, followed by three 50s recordings (10s baseline, 20s green flicker at 10 Hz, 20s recovery). Rigid alignment was applied, followed by automatic vessel segmentation using a U-NET model, and sub-pixel diameter tracking via a peak detection algorithm to measure the vessel diameter at each image. Results: Figure 1 illustrates the vascular dynamics in one subject. In the absence of stimulation (Fig. 1A-B), vessel diameter shows spontaneous modulation from the cardiac cycle (~1 Hz) and vasomotion (~0.1 Hz). With flicker stimulus (Fig.1C-D), an additional dilation component appears, corresponding to a 5% increase in arterial diameter. Figure 1E shows the maximum dilation across subjects without (blue) and with (red) flicker stimulus. The maximum dilation in the flicker case (5.2 ± 1.6%) was significant higher compared to the baseline (1.15 ± 0.7%, P < 0.0001). Figure 1F shows the average NVC response over the population, highlighting a triphasic behavior: 1) rapid initial dilation (reaction time: 0.7 ± 0.2s), followed by a slower dilation to reach the maximum, and a fast post-stimulus contraction around 1.1s after flicker ends. Further details about the characterization of NVC over the population can be found in [8]. We further leveraged the system’s wide FOV to monitor three vessels simultaneously: two arteries and one vein (Fig. 2). Both arteries (Fig. 2B, D) showed synchronized responses; however, artery 1, supplying the fovea (stimulated region), dilated more (6.2%) than artery 3, which perfused a peripheral zone (3.8%). The vein’s response differed markedly from the arteries under both conditions (Fig. 2C), highlighting distinct dynamics between vessel types. Conclusion: Our method enables precise, high-speed measurement of NVC in the living human retina, revealing localized, stimulus-driven vascular responses with cellular-scale resolution. This opens new opportunities for probing early neurovascular dysfunction in retinal diseases, which will be the next step of this study.

Résumé: Full-Field OCT provides high-resolution en-face multi-depth retinal imaging with precise axial sectioning, enabling detailed assessment of retinal nerve fiber layer structures. We present imaging results and an image processing pipeline for quantitative biomarker extraction.