Final answer:
Graves' disease is the most common cause of bilateral proptosis, leading to hyperthyroidism-related eye symptoms like bulging eyes.
Step-by-step explanation:
The most common cause of bilateral proptosis is Graves' disease, also known as thyroid eye disease. This autoimmune disorder affects the thyroid system, leading to hyperthyroidism, which can manifest as proptosis and lid retraction. This condition is also referred to as exophthalmic goiter, characterized by the bulging of the eyeballs out of the face due to hyperthyroidism causing inflammation and tissue buildup in the orbits. Graves' disease is a more prevalent cause of proptosis than conditions like orbital cellulitis, orbital pseudotumor, or other infections like conjunctivitis and blepharitis.