Intraorbital optic nerve path in normal subjects and subjects with glaucoma

Abstract

Purpose : Magnetic resonance imaging (MRI) images were analyzed to characterize the path characteristics of the intraorbital optic nerve (ON) in central gaze and horizontal duction.

Methods : High resolution MRI in 2-mm thick quasi-coronal planes perpendicular to the long axis of each orbit was obtained using surface coils during fixation in central gaze and horizontal duction in normal subjects and subjects with primary open angle glaucoma (POAG) at normal intraocular pressure (IOP). Both eyes of 8 subjects for each group were analyzed. In each image plane, the ON was manually outlined and its centroid converted into 3-D coordinates relative to globe center in a normalized coordinate system. Normalized ON centroid coordinates were then compared with the shortest distance path between the orbital apex and optic nerve-globe junction to produce residuals that were plotted to visualize path deviations from a straight line. Helicoid ON paths were defined as having two or more crossings of the straight line in the horizontal or vertical plane, whereas arc-like ON were defined as having no crossings.

Results : In normal controls, ON path was redundant in central gaze, deviating inferotemporally in central gaze, both nasally and temporally in adduction, and inferotemporally in abduction. Central gaze ON path in controls was arc-like in 9 orbits, helicoid in 6, and indeterminate in 1. In adduction by controls, ON path was arc-like in 9 orbits, helicoid in 5, and indeterminate in 2. In abduction, control ON path was arc-like in 7, helicoid in 6, and indeterminate in 3. In POAG, ON path was more redundant, deviating inferiorly in central gaze, inferonasally in adduction, and inferotemporally in abduction. In central gaze in POAG, 12 ON paths were arc-like, 3 helicoid, and 1 was indeterminate. In adduction in POAG, ON path was arc-like in 10, helicoid in 5, and indeterminate in 1. In abduction in POAG, ON path was arc like in 15 and helicoid in 1. Chi-square testing showed that ON path distribution in abduction was significantly less helicoid and more arc-like in POAG than in controls (p = .0125).

Conclusions : ON paths are helicoid or arc-shaped in both normal subjects, and subjects with POAG at normal IOP, but in abduction ON paths are less helicoid in POAG.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Magnetic resonance imaging (MRI) of the optic nerve path from the orbital apex to the nerve-globe junction.

 

Helicoid (green) and arc-like (red) paths of the ON