Background: The Parks-Bielschowsky three-step test (TST) can incorrectly indicate that a superior oblique muscle is paretic in patients with restrictive strabismus. Although this pitfall in diagnosis has been widely reported, no large studies have examined the incidence of a positive TST in patients with Graves disease.
Methods: We performed a retrospective chart review of 31 consecutive patients with Graves orbitopathy examined at Children's Hospital of Boston from 2003 to 2007. We analyzed ocular ductions, misalignment, and torsion, and thyroid function studies.
Results: Six (20%) of the patients had a positive TST, 3 (10%) of which showed excyclotorsion in at least one eye. However, of the 6 patients, 5 had obvious ocular adnexal signs of Graves disease and 2 had obvious supraduction deficits, leaving only 1 (3%) patient in whom the clinician would have mistakenly diagnosed a superior oblique palsy.
Conclusions: Although a positive TST occurs frequently in Graves disease, other clinical features should allow distinction from superior oblique palsy in most patients.