Vision-threatening thyroid orbital disease--the clinical features.

Thyroid orbital disease may threaten sight when acute proptosis causes corneal exposure or when enlarged extraocular muscles cause compressive optic neuropathy. The early clinical signs of thyroid optic neuropathy include loss of colour perception and visual field defects. The onset of thyroid optic neuropathy is difficult to predict and these clinical tests should be included in the routine examination of patients with thyroid orbital disease.