Axonal pore paths get closer to the optic nerve center with increased depth through the lamina cribrosa

Abstract

Purpose : The lamina cribrosa (LC) has a key role in the pathogenesis of glaucoma. Little is known, however, about the axonal paths through the LC and their relevance to the development of glaucomatous changes. We seek to characterize the axonal paths within the LC, specifically the pores through which the axons pass, by determining pore paths relative to the center of the optic nerve (ON).

Methods : 81 eyes (66 subjects), including 10 healthy, 23 glaucoma suspect (GS), and 48 glaucomatous (GL) eyes, underwent a comprehensive ophthalmic exam and swept-source OCT scanning. The center of the ON head was ascertained by locating the Bruch membrane opening and finding the centroid. LC pores were segmented using a previously described segmentation algorithm. Axonal pore paths were tracked individually across the depth of the LC automatically using custom MATLAB and ImageJ software. Pore paths were then quantified using a method described in Figure A, with positive values for paths traversing the LC towards the center of the ON and negative values for those diverging from the center. Linear mixed effects models were used to test whether average path significantly differed from zero and to quantify the difference between diagnostic categories and disease severity as quantified by VF mean deviation (MD).

Results : Average pore paths within the LC traversed toward the ON center posteriorly for a distance of 22.9±2.8μm between the anterior and posterior surfaces of analyzable LC (p<0.001). For each diagnostic category, the average convergence were 21.4±28.2μm (healthy), 21.4±27.3μm (GS), and 24.0±21.1μm (GL). There was no detectable statistically significant difference between the diagnostic categories or VF MD.

Conclusions : Axonal pore paths traverse the LC closer to the ON center along the depth of the LC regardless of disease severity or diagnostic category. Considering that the scleral canal widens with depth this anatomical configuration could be due to decreasing beam width between axonal pores. This spatial organization of the ON should be considered when assessing LC volumetric microstructure.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

(A) Method of determining whether axonal paths traverse LC closer to the ON center: distance between ON center and the anterior pore subtracted from distance between ON center and the same pore tracked all the way to the posterior surface of analyzable LC. (B) Average pore path by diagnostic category and (C) VF MD.