The volume of the levator superior rectus muscle complex was determined from computed tomography scans of 152 orbits from 76 patients with Graves' ophthalmopathy. Clinically observed lid retraction and lid lag did not correlate with the levator/superior rectus muscle volume and did not correlate with limitation of vertical eye movements or inferior rectus muscle volume. These results do not support previously published hypotheses that muscle hypertrophy or levator/superior rectus muscle overaction secondary to inferior rectus muscle restriction are major causes of lid retraction and lid lag. Local adhesion of the levator muscle to fixed orbital tissues is postulated to be the most likely basis for the characteristic lid retraction and lid lag of Graves' ophthalmopathy.
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