Dysthyroid optic neuropathy without extraocular muscle involvement.

We present three atypical cases of dysthyroid optic neuropathy. The unique feature was progressive visual field loss with normal-sized or minimally enlarged extraocular muscles. Other atypical findings included optic nerves that appeared to be linearly on stretch with only moderate proptosis, good ocular motility, and only mildly reduced central visual acuity and color vision despite severe field loss. These cases responded rapidly to decompressive surgery after failing high-dose corticosteroid therapy. While marked enlargement of the extraocular muscles with apical optic nerve compression has been documented to cause dysthyroid optic neuropathy, another etiology such as short optic nerves on stretch appears to be at work in these atypical cases. Although extraocular muscle enlargement is the most important diagnostic feature and indicator of the severity of Graves' ophthalmology, our atypical cases demonstrate that this sign alone is an inadequate basis for diagnosis and visual prognosis.