Measurement of Normal Diameter of Optic Nerve and Optic Nerve Sheath Using MRI
We aim to establish normal diameters of optic nerve and optic nerve sheath on magnetic resonance imaging. Measurement of optic nerve and optic nerve sheath was done on the 102 volunteers who came for cranial magnetic resonance imaging examination at Thammasat University Hospital. The volunteers were free of orbital disorders or known related diseases that might affect optic nerve or optic nerve sheath and no contraindications in performing in the magnetic resonance imaging study. Diameters of optic nerve and optic nerve sheath at 3 mm and 8 mm in distance behind the eye globe were measured in parallel plane to optic nerve on axial T2-weighted turbo spin echo fat-suppressed sequence. Normal diameters of right/left optic nerve at 3 mm and 8 mm behind the eye globe (mean ± 2standarad deviations) are 2.76 ± 0.66 mm/2.74 ± 0.66 mm and 2.32 ± 0.60 mm/2.31 ± 0.53 mm, respectively. The normal right/left optic nerve sheath diameters at 3 mm and 8 mm behind the eye globe (mean ± 2standarad deviations) are 5.10 ± 1.07 mm/5.13 ± 1.03 mm and 4.38 ± 0.91 mm/ 4.36 ± 0.75 mm, respectively. No correlation present between age and size of optic nerve and optic nerve sheath as well as no difference of optic nerve and optic nerve sheath diameters between both eyes are found. For comparison of optic nerve and optic nerve sheath between males and females, most values show no statistically significant difference except for in the bilateral optic nerve sheath diameters and right optic nerve diameter at 3 mm behind eye globe. Normal diameters of optic nerve and optic nerve sheath at 3 mm and 8 mm from the eye globe were established. This information could be helpful in diagnosis some diseases or in excluding some conditions.
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