graves disease, why does this cause a "staring appearance" biologically?

Answer 1

Exophthalmos or protuberance of the eyes is a diagnostic feature of Grave's disease. It is believed to be caused by the effect of thyroid stimulating hormone on the extra-orbital muscles, which then swell considerably, pushing out one or both eyes. Hyperthyroidism, a factor of Grave's disease, may also cause the eyelid to retract, causing an odd, staring expression known as the "hyperthyroid stare".