Superior ophthalmic vein enlargement and increased muscle index in dysthyroid optic neuropathy.

PURPOSE

To compare superior ophthalmic vein diameter and extraocular muscle index in patients with thyroid eye disease with or without optic neuropathy.

METHODS

High-resolution CT scan images of 40 orbits of 20 patients with history of thyroid eye disease (with or without optic neuropathy), who underwent orbital decompression surgery from January 2007 to November 2009, were retrospectively reviewed. Superior ophthalmic vein diameter was measured in coronal and axial planes. Extraocular muscle index was calculated according to the method proposed by Barrett et al. The clinical diagnosis of optic neuropathy was based on characteristic signs that included afferent pupillary defect, decreased visual acuity, visual field defects, and dyschromatopsia. Orbits were divided in 2 groups based on presence or absence of optic neuropathy.

RESULTS

Superior ophthalmic vein diameter was significantly higher in orbits with concomitant optic neuropathy (mean 2.4 ± 0.4mm, p < 0.0001). Increased muscle index was also related to optic neuropathy (mean 57.9% ± 5.7%, p = 0.0002). Muscle index greater than 50% was present in all patients with dysthyroid optic neuropathy.

CONCLUSIONS

This study suggests that patients with thyroid eye disease with enlarged superior ophthalmic vein and increased extraocular muscle index are more likely to have concomitant optic neuropathy.