In the relaxed position of forward gaze, the upper lid normally covers 3-4mm of the cornea. In Graves' disease, spasm of the striated levator palpebrae superioris results in elevation of the upper lid, with sclera visible above the cornea, and a stare (Fig. 17.29). Increased sympathetic tone due to hyperthyroidism from any cause may contribute to the lid elevation by stimulation of the sympathetically innervated Muller's muscle.
