Optic nerve involvement in dysthyroidism.

Although its prevalence in dysthyroidism is estimated at less than 5%, optic neuropathy should be recognized as a preventable cause of disabling visual loss. Obscured by more obvious external congestive signs, it is usually insidiously progressive and bilateral, but may be acute and unilateral. Neuro-ophthalmic findings are nonspecific (prechiasmal field defects, normal or swollen nerveheads), and the diagnosis should be suspected in the context of typical adnexal changes of dysthyroidism. Optic nerve involvement is probably secondary to apical orbital compression by congested muscles. Treatment with oral corticosteroids, irradiation, or orbital decompression has been beneficial, especially in the early phases.