Study finds, Optic nerve tortuosity and displacements during
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A Study was conducted to assess the morphology and 3-dimensional (3D) displacements of the eye globe and optic nerve (ON) in adduction/abduction using MRI and to assess the differences between healthy emmetropic and highly myopic (HM) subjects.

In main gaze, abduction, and adduction (15°), MRI volumes of both eyes from 18 controls and 20 HM cases were postprocessed. To determine ON tortuosity, all ONs were manually segmented and fitted to a 3D curve. ON displacements were measured in four quasicoronal planes that were 3 mm apart and perpendicular to the ON in primary gaze.

--Axial length was higher in the HM group. Adjusted ON tortuosities (ie, ON tortuosities estimated before myopia onset) were lower in HM eyes versus controls in primary gaze, adduction and abduction for all cases.

--In all eyes, ON displacements in adduction were significantly different from those in abduction in the naso-temporal direction 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.

Finally, the ON's adjusted tortuosity was much lower in HM eyes, implying that eyes destined for HM had larger ON traction forces during eye movements prior to the start of myopia. This ON measure could be useful in determining whether there is a relationship between eye movements and axial elongation.