Unilateral ONSF may be sufficient in IIH patients with bilateral visual loss, papilledema

The authors conducted this retrospective chart review to evaluate the effect on papilledema grade of optic nerve sheath fenestration (ONSF) in operated eyes and contralateral nonoperated fellow eyes of patients with idiopathic intracranial hypertension (IIH). They found that unilateral ONSF significantly decreased the grade of papilledema in both ipsilateral operated and contralateral nonoperated eyes. This suggests that bilateral ONSF may not always be necessary in patients with bilateral visual loss.

The charts of 78 patients with idiopathic intracranial hypertension (IIH) who underwent ONSF at one hospital were reviewed. Sixty-two of them had unilateral ONSF; 10 had bilateral ONSF. Twenty IIH patients who did not undergo surgery served as controls. Optic disc photographs were graded by a masked observer using the Frisén papilledema grading scale at preoperative baseline and postoperatively through 12 months of follow-up. Wilcoxon signed-rank test was used to examine the change in papilledema grade in both operated and nonoperated eyes at each time point.

The median grade of papilledema for operated and nonoperated eyes was 3 and 2, respectively, at baseline. Postoperatively, the grade was 2 in each eye at two weeks (P < 0.0001 and < 0.0002 for operated and nonoperated eyes, respectively), 1 in each eye at three months (P < 0.0001 for both operated and nonoperated eyes), 1 in each eye at six months (P < 0.0001 for both operated and nonoperated eyes) and 0.5 and 1 for operated and nonoperated eyes, respectively, at 12 months (P < 0.0001 for both operated and nonoperated eyes). The control group also showed significant changes in edema score at follow-up in both eyes, but there was no significant difference in the change in edema score between the two eyes. Visual acuity improved significantly after unilateral ONSF in both operated and nonoperated eyes (P = 0.005 and 0.026, respectively), as did visual field (P = 0.017 and 0.009, respectively, after 12 months).

After unilateral ONSF, the majority of patients in the study group experienced improved visual function in both operated and nonoperated eyes. The authors say that the reduction in disc edema and visual stabilization was clinically sufficient to obviate the need to proceed with a contralateral ONSF in the majority of patients. They say that the mechanism for this contralateral surgical effect is not certain and could be related to decreased intrasheath cerebrospinal fluid in both optic nerves after unilateral ONSF, regression toward the mean, spontaneous improvement or simply better patient compliance with maximum medical therapy after unilateral surgery.