Optic nerve tortuosity and displacements during horizontal eye movements in healthy and highly myopic subjects

Abstract

ABSTRACTPurpose(1) To assess the morphology and 3D displacements of the eye globe and optic nerve (ON) in adduction/abduction using magnetic resonance imaging (MRI). (2) To assess differences between healthy emmetropic and highly myopic (HM) subjects.MethodsMRI volumes of both eyes from 18 controls and 20 HM subjects in primary gaze, abduction and adduction (15°) were postprocessed. All ONs were manually-segmented and fitted to a 3D curve to assess ON tortuosity. ON displacements were evaluated in 4 quasicoronal planes which were perpendicular to the ON in primary gaze and 3 mm apart.ResultsAxial length was higher in the HM group (28.62±2.60 vs 22.84±0.89 mm; p<0.0001). Adjusted ON tortuosities (i.e., ON tortuosities estimated before myopia onset) were lower in HM eyes (0.9063±0.0591) versus controls (1.0152±0.02981) in primary gaze, adduction (0.9023±0.05538 versus 1.0137±0.0299) and abduction (0.9100±0.0594 versus 1.0182±0.0316); p<0.0001 for all cases. In all eyes, ON displacements in adduction were significantly different from those in abduction in the naso-temporal direction (p<0.0001 in all planes) but not in the supero-inferior direction. ON displacements in the posterior segments of the ON were smaller in the HM group in both gaze directions and were larger in the anterior-most ON segment in adduction only.ConclusionsThe adjusted tortuosity of the ON was significantly lower in HM eyes, suggesting that eyes destined toward HM exhibited higher ON traction forces during eye movements before the onset of myopia. Our ON metrics may be valuable to explore a potential link between eye movements and axial elongation.