PURPOSE: To describe corneal astigmatism in patients under the age of 55 years with Graves' ophthalmopathy and to compare it to a control group. METHODS: Retrospective, nonrandomized comparative observational case series. A total of 109 patients with inactive Graves' ophthalmopathy and 109 age- and gender-matched control individuals without Graves' ophthalmopathy were examined with manual corneal keratometry. In the Graves' patients, 52% had a CT scan available for review, and 41% underwent orbital, strabismus, and/or eyelid surgery with a follow-up of keratometry over a mean period of 1.7 years after surgery. RESULTS: For the dioptres, there was a statistically significant difference between the Graves' and the control eyes at 3-3.25 dioptres in both eyes (t-test, right eyes, P=0.042; left eyes, P=0.041). For the meridians, the astigmatism was found to be greater at the meridians 95-100 degrees (t-test, P=0.044) and 105 degrees -110 degrees (t-test, P=0.017) in the right eyes only. In 10 (9%) Graves' patients, the astigmatism had caused newly acquired reduced visual acuity. Greater astigmatism in dioptres did not correlate with specific CT scan findings (chi(2)-test, df=2, P=0.187). Following orbital, strabismus, and eyelid surgery, the dioptres and meridians of the astigmatism did not change in 56 (68%) and 66 (81%) eyes, respectively. CONCLUSIONS: Graves' ophthalmopathy may be associated with greater with-the-rule corneal astigmatism, which, overall, is not influenced by orbital, strabismus, or eyelid surgery. The astigmatism may possibly be caused by soft-tissue fibrosis in the superolateral orbital region.