The Optic Canal Size Is Associated With the Severity of Papilledema and Poor Visual Function in Idiopathic Intracranial Hypertension

To determine whether the size of the bony optic canal is associated with the severity of papilledema and poor visual function in idiopathic intracranial hypertension (IIH).

We performed a retrospective review of definite patients with IIH with requisite brain magnetic resonance imaging allowing for optic canal measurement. Clinical characteristics and automated (Humphrey) visual field results were reviewed; papilledema was graded according to the modified Frisén scale. Cross-sectional area of the optic canals was measured independently by 2 readers and averaged for each canal. Logistic regression modeling was applied.

Sixty-nine patients with IIH were included (mean age: 33; 91% women; 65% black). Controlling for age, sex, body mass index, race, and cerebrospinal fluid (CSF) opening pressure, each mm increase in canal size was associated with a 0.50 dB reduction in Humphrey visual field mean deviation (P = 0.006); this was likely mediated by the increased odds of Grade 4-5 papilledema or optic atrophy in patients with larger canals (odds ratio: 1.30 [95% CI: 1.10-1.55; P = 0.003] for Grade 4-5 papilledema or atrophy vs grade <4 papilledema per mm increase in canal size).

Poor visual function and severe papilledema or optic atrophy were associated with a larger optic canal. Potential mechanisms include alteration of local CSF flow or bony remodeling at the optic canals.