Aims (1) To assess the morphology and 3-dimensional (3D) displacements of the eye globe and optic nerve (ON) in adduction/abduction using MRI. (2) To assess differences between healthy emmetropic and highly myopic (HM) subjects.
Methods MRI 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 four quasicoronal planes which were perpendicular to the ON in primary gaze and were 3 mm apart.
Results Axial length was higher in the HM group (28.62±2.60 vs 22.84±0.89 mm; p<0.0001). Adjusted ON tortuosities (ie, 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 vs 1.0137±0.0299) and abduction (0.9100±0.0594 vs 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.
Conclusion The adjusted tortuosity of the ON was significantly lower in HM eyes, suggesting that eyes destined towards 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.
- optic nerve
Data availability statement
Derived data supporting the findings of this study are available from the corresponding authors on reasonable request.
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QVH and MJG contributed equally.
Contributors Design of study: XW, QVH and MJAG. Collection and management of data: XW, JG, SC, LAY, KBF, QVH and MJAG. Analysis and interpretation of data: XW, JG, QVH and MJAG. Preparation of manuscript: XW, QVH and MJAG. Review or approval of manuscript: QVH and MJAG.
Funding The study was supported by the National Natural Science Foundation of China (12002025 (XW)), by the Singapore Ministry of Education Academic Research Funds Tier 1 (R-397-000-294-114 (MG)) and Tier 2 (R-397-000-280-112 and R-397-000-308-112 (MG)), by K08 Grant (QVH, 1 K08 EY023595, National Eye Institute, NIH), the Louis V. Gerstner Jr. Scholars Career Development Award (QVH; Grant number: none), Clinician Scientist Award (QVH, CSA-INVMay0011, National Medical Research Council, Singapore), philanthropic donation from John Cushman (QVH) and The Macula Foundation, New York, New York, USA (LAY). The sponsor or funding organisation had no role in the design or conduct of this research.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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