The effects of optic nerve sheath fenestration on visual function and OCT metrics in idiopathic intracranial hypertension: a retrospective study

Background Idiopathic intracranial hypertension (IIH) is characterized by elevated intracranial pressure (ICP) without an identifiable cause and may lead to optic nerve damage and permanent vision loss. We evaluated longitudinal structural and functional outcomes after optic nerve sheath fenestration (ONSF) and how Optical Coherence Tomography (OCT)–visual function relationships evolve over early postoperative follow-up. Methods This retrospective case series included 35 patients (70 eyes) with IIH who underwent bilateral ONSF. Structural and functional measures were assessed at baseline and at 6, 12, and 24 weeks postoperatively, including best-corrected visual acuity (BCVA) recorded on a 0–10 decimal chart, standard automated perimetry indices (mean deviation (MD), visual field index (VFI, pattern standard deviation), and spectral-domain OCT metrics (peripapillary retinal nerve fiber layer (RNFL) thickness and macular ganglion cell layer (GCL) measures. Pearson correlations were used to evaluate associations between OCT parameters and visual function at each time point. Results OCT demonstrated significant reductions in optic nerve head swelling measures and peripapillary RNFL thickness over time (p 0.05), consistent with postoperative improvement in papilledema. Macular GCL metrics also declined over follow-up, which may reflect delayed neuroaxonal loss and/or unmasking as edema resolves rather than edema resolution alone. BCVA and MD improved over follow-up, with several endpoints showing the largest change by approximately 12 weeks followed by stabilization through 24 weeks. Correlations between RNFL/macular metrics and visual field indices (VFI and MD) strengthened over time and were strongest by 24 weeks, consistent with increasing structure–function concordance as postoperative edema improves. Cup volume did not show statistically significant change. Conclusion ONSF was associated with improvement in papilledema-related structural measures and visual function in vision-threatening IIH. OCT-derived parameters, particularly RNFL and macular ganglion cell metrics, are useful for longitudinal postoperative monitoring; early RNFL values may be confounded by edema, while later measurements better reflect axonal status and align more closely with visual function.