The diagnosis of Graves' disease, aside from a history of thyroid problems, uses measures of visual acuity, pupillary light responses, and ocular motility. The configuration and movement of the lid margins should be carefully studied. The slit-lamp examination should include the measure of intraocular pressure by applanation tonometry both in downgaze and in the primary position. Because of the foreshortened rectus muscle's traction on the globe, attempts to force the eye into the primary position often result in a marked, though transient, elevation of the intraocular pressure. Visual field testing and a sonographic determination of rectus muscle thickness by A-scan complete the workup. Echographic confirmation of rectus muscle thickening in the midportions of muscle belly, but with no thickening at the tendinous insertions, is characteristic of Graves' disease and differentiates it from orbital myositis, in which the inflammatory swelling extends all the way to the point of insertion. In cases that remain in doubt as to the correct diagnosis, a thin-section CT scan of the orbit helps to rule out a mass lesion other than one or more swollen muscles. High-resolution MRI scanning with determination of the T2-relaxation time produces images that can be used to judge the water content in the rectus muscles, a correlate for inflammatory edema.
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