Exophthalmos is a symptom of an underlying medical condition in which the eyes protrude out of their sockets. It is characterized by an abnormally large appearance of the eyes and can be accompanied by redness, watering, and a feeling of pressure. It develops gradually over time, but in some cases can be sudden. Exophthalmos can be caused by a variety of conditions, including Graves' disease, thyroid eye disease, and tumors.