Ophthalmopathy, particularly its infiltrative form, is considered a characteristic feature of Graves' disease. However many other also life-treating conditions may be manifested as unilateral exophthalmos and lead to diagnostic problems. A case of a sixty six-year old patient with asymmetric exophthalmos and rapidly decreasing vision acuity is reported. Thyroid eye disease was suspected due to clinical symptoms (diplopy, impaired right eye motion) and thickening of extraocular muscles in ultrasound imaging. Further follow-up and orbits as well as head MRI imaging led to the final diagnosis of cavernous sinus thrombosis, complication of acute maxillary sinusitis.