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Jake Hillard; Neuro-scleral Canal Size in Veterans with and without Glaucoma. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5909.
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© ARVO (1962-2015); The Authors (2016-present)
Deep optic nerve structures have been implicated in the pathophysiology of glaucoma, but the area posterior to Bruch's membrane and anterior to the lamina cribrosa (Neuro-scleral canal or NSC) is not often dicussed in humans. This area has been shown to expand in experimental glaucoma in monkeys. This prospective, cross-sectional study tested if glaucomatous optic nerves have larger NSC sizes than non-glaucomatous nerves.
Veterans presenting for eye exams were recruited for study. SD-OCT scans were obtained from one eye of each subject. Magnification and the fovea-BMO angle (FoBMO) were accounted for. 18 subjects without glaucoma (GRP 1) (mean age: 65) and 7 with controlled open angle glaucoma (GRP 2) (mean age: 75) qualified for examination of deep nerve structures. The maximum diameter of the NSC was measured, and it's orientation was noted (see figures 1 and 2). The NSC diameter 90 degrees from that plane was also measured. T-tests (non-parametric when needed) compared the mean maximum diameter of the NSC from each group, then again after correcting for individual BMO diameter, and the maximum NSC diameter was compared to the NSC diameter 90 degrees from it pooling both groups.
Results are given as avg (SD). The raw maximum NSC diameter was GRP1= 1723 mm (205) ; GRP2= 2018 mm (239) (p<0.01). BMO area was GRP1= 1.60 mm2 (0.3); GRP2= 2.33mm2 (0.5). The ratio of maximum NSC diameter to BMO size was GRP1= 1.2 (0.13); GRP2= 1.2 (0.07) (P=.41). Comparing the max NSC diameter in all subjects vs NSC diameters 90 degrees from that plane, there was a significant difference (P=0.013). The direction of maximum outpouching was superior nasal in GRP1= 56%; GRP2= 71%. BMO and NSC size were significantly correlated (p<0.001, R2 =.58).
There were significant differences in the sizes of the NSC of the non-glaucomatous and glaucomatous veterans that did not persist when BMO size was taken into account. BMO and NSC size were significantly correlated. NSC was wider than BMO in all subjects. NSC showed the most "outpouching" in the superior nasal quadrant. A larger population is required to test if the size and direction of NSC outpouching may have implications in an individual’s risk of developing glaucoma. Correlation with visual field defects (controlling for BMO size) may give insight to the implications NSC morphology has on the regional risk of glaucomatous damage to retinal nerve fibers.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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