Optic Nerve Sheath Diameter Assessment and its Association with Eyeball Transverse Diameter on 1.5T in Healthy Adults

Imaging evaluation of the anterior visual pathway, particularly the structures like optic nerves (ON) and optic nerve sheath diameter (ONSD), requires knowledge of standard dimensions. Apart from clinical and ophthalmoscopic evaluation, imaging, especially MRI, plays an essential role in the complete evaluation of optic nerve and the entire visual pathway. The ONSD has been found to have a competent correlation with intracranial pressure (ICP) can be used as an indirect marker of intracranial hypo or hypertension. The normal limits of ONSD as measured using T2 weighted MR images and its correlation with clinical parameters and the eyeball transverse Diameter (ETD) needs standardization. Our secondary objective is to deduce the ONSD assessed at different depths (3, 6, or 9 mm) and arrive at a ratio of the ONSD and eyeball transverse diameter (ETD) which are better correlated with ICP. The data serves as a baseline standard for comparison of ONSD in patients of various age groups and to further quantify the technique of measuring the ONSD. Results: In general, ONSD of the general population is independent of age, sex and has any mean of 4.7mm. There is no significant variation in the ONSD measured at a depth 6mm, and 9mm from the globe. A convincing correlation between the ETD and ONSD was noticed in the form of ONSD/ETD with a mean value of 0.22. Conclusion: This study determined a range of MRI-based ONSD in healthy Indian adults. There was a strong association between the ETD and ONSD, which can be presented as the ONSD/ETD ratio. Our study suggests that the ONSD/ETD ratio is a more reliable indicator than ONSD itself; if this correlation is maintained in disease populations needs to be investigated further