Cup-to-disc ratio in patients with idiopathic intracranial hypertension is smaller than that in normal subjects.

Background: A small cup-to-disc (C:D) ratio is an established risk factor for nonarteritic anterior ischemic optic neuropathy. We sought to determine if a small C:D ratio was present in patients with idiopathic intracranial hypertension (IIH) as a potential risk factor for visual loss in that disorder.

Methods: We performed a retrospective review of 52 charts of patients diagnosed with IIH at Michigan State University from 1990 to 2003. Twenty-eight patients (55 eyes) met diagnostic inclusion criteria and had undergone fundus photography of sufficient quality to allow assessment of the C:D ratio after optic disc edema had become minimal or resolved. C:D ratio was measured from the digitized photographs. The data were placed into rank order categories (0.1 unit intervals) and compared to published normative C:D data.

Results: The average vertical C:D ratio was 0.143 (SD 0.061) in the right eye and 0.127 (SD 0.056) in the left eye. The average horizontal C:D ratio was 0.145 (SD 0.053) in the right eye and 0.133 (SD 0.053) in the left eye. The IIH group rank distribution data were compared to published normative C:D ratio data (chi-square test). In each case, the IIH population had a statistically significantly smaller C:D ratio (P < 0.0001) compared to normal subjects.

Conclusions: The C:D ratio in our IIH population was smaller than that in published control populations. A small C:D ratio may lower the threshold for developing optic disc edema from ischemia, increased intracranial pressure, or other mechanisms. Additional studies are needed to confirm these findings.