Optic nerve sheath diameter as a surrogate for intracranial pressure: a noninvasive follow-up strategy using ocular ultrasonography

Background: Idiopathic intracranial hypertension (IIH), characterized by increased intracranial pressure (ICP) without a clear cause, typically affects obese women of reproductive age. Although lumbar puncture (LP) is diagnostic, its invasiveness limits its repeated use. Consequently, a non-invasive alternative is essential. Therefore, we assessed whether optic nerve sheath diameter (ONSD) measurement via orbital ultrasonography could serve as an alternative method for monitoring changes in ICP in patients with IIH. Methods: In this prospective observational study, patients with IIH, diagnosed using the modified Dandy criteria, underwent ONSD assessment using B-scan ultrasonography. Bilateral measurements were performed 3 mm posterior to the optic disc with the probe and sterile gel placed on the closed upper eyelid. ONSD was recorded before LP and one month after initiation of medical treatment. Comprehensive ophthalmologic examinations were also conducted. Patients with ocular pathology, neuroimaging abnormalities, or contraindications to LP were excluded. Results: Twenty-four eyes from 12 female patients with IIH were evaluated. The mean (standard deviation [SD]) age was 27.3 (6.9) years, and the mean ICP was 34.8 (10.3) cm H2O. Although the ONSD decreased one month after LP, changes in mean ONSD of the right eye, left eye, and their average were not statistically significant (all P > 0.05). No significant correlations were observed between baseline ICP and ONSD values (all P > 0.05). Conclusion: Although ONSD measurement via ultrasonography provides a noninvasive method for assessing ICP in IIH, our findings revealed no significant change one month after treatment initiation. ONSD may gradually decrease following LP; however, a return to baseline values appears to require a prolonged period, even after ICP normalization. This should be considered during patient follow-up. Our findings underscore the limitations of using ONSD as a standalone marker for monitoring therapeutic response. Further research is warranted to explore the factors influencing ONSD dynamics and to establish standardized, patient-centered measurement protocols.