Lamina cribrosa pore tortuosity in healthy and glaucomatous eyes

Abstract

Purpose : The lamina cribrosa (LC) is hypothesized to play an important role in the pathogenesis of glaucoma, with impairment to the axoplasmic flow as a leading mechanism for damage. Yet, the path ganglion cell axons take through the LC, which may affect axoplasmic flow, remains poorly characterized. A more tortuous path through the LC may interfere with axoplasmic flow, increasing the risk of glaucoma damage. The purpose of this study was to investigate in vivo the hypothesis that axons of glaucoma eyes take a more tortuous path through the LC compared to healthy eyes.

Methods : 10 healthy (H), 23 glaucoma suspect (GS) and 48 glaucoma (GL) eyes from 66 subjects were scanned using a swept source (SS-)OCT system. All subjects underwent a comprehensive ophthalmic exam and diagnosed based on optic nerve appearance and visual field. The LC pores were automatically segmented using a previously described segmentation algorithm. Individual pore paths were automatically tracked through the depth of the LC using a custom MATLAB and ImageJ software (Fig A-B). Pore tortuosity, defined in Fig C, was quantified for each eye. A linear mixed effect model was used to identify differences in pore tortuosity between diagnostic categories as well as with VF MD. A Kolmogorov–Smirnov test was used to determine difference in variance between diagnostic categories.

Results : Pore tortuosity in GL eyes (1.46±0.08) was significantly higher than in H (1.40±0.04, p=0.03) and GS eyes (1.39±0.07, <0.01) (Fig D). GL eyes also had larger variances compared to H and GS (p=0.02, <0.01, respectively) (Fig E). Glaucoma severity, as determined by VF MD, was not associated with pore tortuosity (Fig F).

Conclusions : Axons of GL eyes take a more tortuous path through the LC compared to those of H eyes. Furthermore, the tortuosity of GL eyes is more variable than those of H eyes. The causality of the relationship between pore tortuosity and glaucoma damage, as assessed by visual fields, warrants further investigation.

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

 

(A) SS-OCT en face of the LC with (B) a subset of pore paths traced shown in 3D. (C) Method of assessing pore tortuosity – divide the path length through pore centroids (red) by the distance between the top and bottom pore (purple). (D) Boxplot and (E) density distribution of pore tortuosity grouped by diagnostic category (H – green, GS – blue, GL – red). (F) Scatter plot of tortuosity according to VF MD.