In thyrotoxicosis the increase in sympathetic activity due to increased T3 and T4 leads to contraction of Muller's muscle. Hence these patients would have infrequent blinking and infact some of them might sleep with their eyes open leading to corneal erosions. Lid retraction, causing a staring appearance, can occur in any form of thyrotoxicosis and is the result of sympathetic overactivity. However, Graves' disease is associated with specific eye signs that comprise Graves' ophthalmopathy. The earliest manifestations of ophthalmopathy are usually a sensation of grittiness, eye discomfo, and excess tearing. The most serious manifestation is compression of the optic nerve at the apex of the orbit, leading to papilledema; peripheral field defects; and, if left untreated, permanent loss of vision.