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Bryn Brazile, Bin Yang, Andrew Voorhees, Ian A Sigal; Simultaneous in-situ visualization and quantification of lamina cribrosa collagen beams and capillaries at normal and elevated IOPs. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1220. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
There is a clinical association between glaucoma and systemic capillary abnormalities, (Pasquale et al, IOVS 2015); however, almost nothing is known about the morphology and topology of the capillaries in the lamina cribrosa (LC), or how they are affected by IOP. Our goal was to visualize the LC capillaries, measure their tortuosity and determine the changes with elevated IOP.
Three pig eyes (6 months old) were perfused with 50ml of a fluorescent dye through the external ophthalmic artery within 8 hours of death. Eyes were excised and the posterior half mounted in a custom-made inflation chamber for control of IOP and simultaneous viewing of the LC. Images were acquired at IOPs of 15, 25 and 40 mmHg using structured illumination to visualize the collagen and fluorescence to visualize the capillaries. We measured the tortuosity of the capillaries between vessel branches using FIJI. Paired t-tests were used to determine if LC capillary tortuosity changed significantly with elevated IOP.
120 vessel segments were measured. Capillaries were highly tortuous at 15 mmHg (up to 1.35), with surprisingly different topology from the beams (Fig 1). There was a trend towards decreased tortuosity in all three eyes as IOP increased from 15 mmHg to 25 mmHg (p >0.05). Tortuosity decreased significantly for IOP increased from 15 mmHg to 40 mmHg (p<0.01).
Overall tortuosity decreased as IOP increased, but some capillary segments did become more tortuous. While tortuosity in capillaries is often regarded as problematic because it may reduce blood flow, the higher tortuosity at 15 mmHg may provide “slack” that protects the capillaries from over-stretch damage under elevated IOP. We, thus, speculate that low tortuosity capillaries could be a risk factor for damage under high IOP.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Fig 1: A) lamina cribrosa, B) overlay of capillaries (red) and collagen beams (green) and C) capillaries at 15mmHg (red) and 45mmHg (green)
Fig 2: Tortuosities decreased with IOP as A) Box and B) Bland-Altman plots
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