Diplopia in autoimmune thyroid disease.

Diplopia without obvious exophthalmos, caused by infiltrative endocrine ophthalmopathy, developed in 12 patients with clinical and laboratory confirmation of autoimmune thyroid disease. In eight patients, the diplopia alone prompted medical attention, which led to the diagnosis of autoimmune thyroid disease. A hypotropia secondary to restrictive tightening of the inferior rectus muscle, producing vertical diplopia, was the most common manifestation of the disorder. The ocular muscle imbalance in autoimmune thyroid disease is caused by mechanical orbital restriction of the extraocular muscle, not by an innervational defect. Evidence of orbital restriction of the eye muscles can establish the diagnosis, regardless of the patient's thyroid function.