Abstract
Purpose :
Retinal vasculature is readily visualized with ophthalmoscopy, enabling direct assessment of vascular diseases. The reaction of vasculature to metabolic demand, known as neurovascular coupling, is an indirect measure of retinal function. Here we assessed the variability of diameter changes along a vessel in response to a stimulus using an adaptive optics scanning light ophthalmoscope (AOSLO).
Methods :
Split-detector images of the vasculature using a 1x1° field of view were obtained from 3 subjects with no known retinal pathology. Imaging locations were determined by an estimate of maximum retinal ganglion cell (RGC) density and arteriole presence using OCT-based RGC thickness measurements. A shuttered, 15Hz stimulus was coupled into our AOSLO and targeted at the fovea (E=0.5µW; λ=556nm; r=0.75°). To ensure foveal overlap, subjects adjusted the stimulation source to overlap with the target. Imaging was done by taking at least 6 control videos, followed by 2 trials of at least 6 stimulation videos with a 1.5 minute break in between, for overall total of 65 videos. All AOSLO videos were registered using a strip-based approach and montaged. Following processing, all montaged images were opened in ImageJ and combined into a stack. Vessel diameters in pixels were recorded using the measure tool in ImageJ by one grader (BB). Four locations along each vessel were measured in all montaged images: top, above-middle, below-middle, and bottom of the vessel. The diameters were then averaged, and stimulus images were subtracted from controls to obtain the absolute change in diameter for each vessel section (summarized in Table 1).
Results :
The average (± std dev) diameter change of chosen vessels between conditions was 1±0.5µm, corresponding to a percent change of 5.5±3.2%, and consistent with prior reports. We observed a substantial range of diameter changes (range: 0.2 to 1.9µm) across all measurement locations. Along individual subjects’ vessels, we observed substantial variation (range: 0.7 to 1.5µm or 2.8 to 8.7%).
Conclusions :
This work describes the normative variability of vascular diameter for neurovascular coupling in the retina. We observed substantial variation in the stimulus-evoked changes in vascular diameter both across and within all 3 subjects; future work will determine the source of this variability.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.