Final answer:
Exophthalmos is a sign of hyperthyroidism, specifically associated with Graves disease.
Step-by-step explanation:
Exophthalmos is a sign of hyperthyroidism. Specifically, it is associated with a condition called Graves disease, which is the most common cause of hyperthyroidism in the United States. Graves disease is characterized by symptoms such as heat intolerance, rapid and irregular heartbeat, weight loss, goiter (a swollen thyroid gland), and exophthalmia (bulging eyes), also known as Graves ophthalmopathy.