Lamina cribrosa vessel and collagen beam networks are distinct

Highlights

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We combined fluorescence and polarized light microscopy to 3D map lamina cribrosa vessels and collagen beams in monkey eyes.

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Collagen beam and vessel networks of the lamina cribrosa have distinct topologies.

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Over half of lamina cribrosa collagen beams did not contain a blood vessel.

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One fifth of blood vessels in the lamina cribrosa were outside collagen beams.

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Beams with/without vessels and vessels inside/outside beams may respond differently to IOP.

Abstract

Our goal was to analyze the spatial interrelation between vascular and collagen networks in the lamina cribrosa (LC). Specifically, we quantified the percentages of collagen beams with/without vessels and of vessels inside/outside of collagen beams. To do this, the vasculature of six normal monkey eyes was labeled by perfusion post-mortem. After enucleation, coronal cryosections through the LC were imaged using fluorescence and polarized light microscopy to visualize the blood vessels and collagen beams, respectively. The images were registered to form 3D volumes. Beams and vessels were segmented, and their spatial interrelationship was quantified in 3D. We found that 22% of the beams contained a vessel (range 14%–32%), and 21% of vessels were outside beams (13%–36%). Stated differently, 78% of beams did not contain a vessel (68%–86%), and 79% of vessels were inside a beam (64%–87%). Individual monkeys differed significantly in the fraction of vessels outside beams (p < 0.01 by linear mixed effect analysis), but not in the fraction of beams with vessels (p > 0.05). There were no significant differences between contralateral eyes in the percent of beams with vessels and of vessels outside beams (p > 0.05). Our results show that the vascular and collagenous networks of the LC in monkey are clearly distinct, and the historical notions that each LC beam contains a vessel and all vessels are within beams are inaccurate. We postulate that vessels outside beams may be relatively more vulnerable to mechanical compression by elevated IOP than are vessels shielded inside of beams.