Walsh & Hoyt: Thyroid Eye Disease

Approximately 6% of patients with thyroid eye disease develop evidence of a compressive optic neuropathy, some associated with optic disc swelling. Dysthyroid optic neuropathy is a compressive optic neuropathy caused by pressure on the optic nerve by enlarged extraocular muscles. In such patients, congestive symptoms almost always precede visual loss, which is usually bilateral, symmetric, and gradual in onset. Of the 36 eyes of 21 patients with dysthyroid optic neuropathy examined by Trobe et al., 12 (33%) had mild to marked disc swelling. Presenting visual acuities were 20/60 or worse in these patients, who usually had central scotomas, often combined with arcuate defects. Kennerdell et al.emphasized the compressive etiology of the optic neuropathy in their report of the CT findings in seven patients with dysthyroid optic neuropathy, four of whom had evidence of optic disc swelling. In all cases, there was moderate to severe enlargement of the extraocular muscles at the orbital apex. Direct measurement of orbital pressure and tissue compliance through manometry demonstrates higher orbital tissue tension and lower orbital compliance in patients with thyroid eye disease. Optic neuropathy can even occur as a late complication several years after initial presentation without evidence of progressive orbitopathy or recurrent inflammation.