April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Imaging localized neurovascular coupling in the normal human retinal microvasculature
Author Affiliations & Notes
  • Angelina Duan
    Department of Optometry & Vision Sciences, University of Melbourne, Parkville, VIC, Australia
  • Phillip A Bedggood
    Department of Optometry & Vision Sciences, University of Melbourne, Parkville, VIC, Australia
  • Bang V Bui
    Department of Optometry & Vision Sciences, University of Melbourne, Parkville, VIC, Australia
  • Andrew B Metha
    Department of Optometry & Vision Sciences, University of Melbourne, Parkville, VIC, Australia
  • Footnotes
    Commercial Relationships Angelina Duan, None; Phillip Bedggood, None; Bang Bui, None; Andrew Metha, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 2605. doi:
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    • Get Citation

      Angelina Duan, Phillip A Bedggood, Bang V Bui, Andrew B Metha; Imaging localized neurovascular coupling in the normal human retinal microvasculature. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2605.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

To quantify changes in the diameter in retinal vessels of < 28 µm diameter in response to local flicker stimulation.

 
Methods
 

The foveal microvascular network was imaged in 3 healthy subjects with a flood-based adaptive optics ophthalmoscope. Each 1.25° imaged region was selected so as to contain a “major” arteriole or venule (~18-28 µm diameter) and associated branches of varying size. Image sequences were collected a) Following 30 seconds of fixation on a static, dimly illuminated grid; b) Following 30 seconds of fixation during which the 593 ± 25 nm (FWHM) imaging light was flickered at 8 Hz on a low power setting (5 µW, cf. 0.5 mW for imaging) for 30 seconds. Five image sequences were collected in each area (200 fps, 80 frames), separated by a resting period of 2 minutes. Acquired sequences were flat-fielded, co-registered and averaged. Vessel diameter was measured semi-automatically, using custom Matlab software: Straight-line regions 4-60 μm in length were traced manually and used to generate intensity cross-sections spaced 0.5 µm apart. In each cross-section, vessel edges were located by finding a maximum in the local image intensity gradient (Prewitt filter). Vessel segments ranging from 6.5 - 28 µm in diameter were measured.

 
Results
 

For the venules, functional dilatation was measurable in segments as small as 13 µm (mean ± SEM = 13.2 ± 2.9%). Local differences in the response were observed along the same venule, e.g. ranging from 5.8 ± 1.1% to 13.4 ± 3.4%. For the arterioles, functional constriction was observed. As with the venules, vessel diameter changes appeared to be localized along the vessel length, ranging from -2.4 ± 1.4% to -13.3 ± 1.4%. The largest constrictions observed were immediately upstream of branch points, which may corroborate evidence of pericyte-mediated neurovascular coupling in peri-capillary vessels reported recently in the literature.

 
Conclusions
 

The diameters of the smallest arterioles and venules in the retina can be modulated in response to functional stimulation. Venules were observed to dilate, while arterioles constricted. The highly focal nature of the response, together with the large magnitude compared with that previously measured in larger vessels, suggest an active local mechanism.

 
 
Figure 1a) Venule after flicker stimulation. Figure 1b) Venule at baseline, before flicker stimulation.
 
Figure 1a) Venule after flicker stimulation. Figure 1b) Venule at baseline, before flicker stimulation.
 
Keywords: 436 blood supply • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 551 imaging/image analysis: non-clinical  
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