Assessment of Optic Nerve and Extraocular Muscle Morphology by Using 1.5 Tesla Magnetic Resonance Imaging

Abstract

The optic nerve and extraocular muscles (EOMs) are fundamental components of the human visual system. Any variation in their morphology may lead to significant ophthalmic and neurological consequences. Magnetic Resonance Imaging (MRI) has emerged as the most reliable non-invasive imaging modality for assessing orbital structures due to its superior soft tissue contrast and multiplanar capability. This study aimed to evaluate the morphology of the optic nerve and EOMs using 1.5 Tesla MRI and to establish normative data among healthy adults in the Indian population. Methods: A retrospective cross-sectional study was carried out at Santosh Hospital, Ghaziabad, involving 74 healthy subjects (37 males, 37 females) aged between 20 and 70 years. MRI scans were acquired using a 1.5 Tesla system with standard head coil. Axial and coronal T1- and T2-weighted sequences were analyzed for optic nerve and EOM dimensions. Measurements were made using DICOM viewing software. Statistical analyses included t-tests, ANOVA, and Pearson correlations to evaluate gender and laterality differences. Results: The mean optic nerve diameter was 2.45 ± 0.56 mm on the right and 2.36 ± 0.56 mm on the left. The mean widths of the lateral rectus and medial rectus muscles were 1.14 ± 0.48 mm and 1.27 ± 0.48 mm respectively on the right side. Males showed slightly higher mean values than females, with significant differences noted for the right optic nerve (p < 0.05). A strong correlation was observed between the right and left optic nerve diameters (r = 0.857, p < 0.01) and between corresponding EOMs (r > 0.68, p < 0.01). Conclusion: MRI provides accurate morphometric data for optic nerve and EOM evaluation. These normative findings are essential for diagnosing orbital and neuro-ophthalmic conditions. Further studies using advanced MRI techniques such as diffusion tensor imaging and high-field systems are recommended to refine diagnostic accuracy and detect microstructural alterations.