What is exophthalmos?

Exophthalmos refers to the condition in which the eyes bulge outward, which is why the correct answer is that it is the bulging outward of the eyes. This can occur due to various conditions, one of the most common being Graves' disease, which is an autoimmune disorder that leads to an overactive thyroid and can cause inflammation and swelling in the eye muscles and surrounding tissues. This eye displacement can also be associated with increased pressure behind the eyeball, but the defining characteristic is the outward bulging itself.

The other options relate to different ocular problems or conditions. Increased eye pressure typically relates to glaucoma, which does not involve bulging eyes but rather pressure exerted within the eyeball. Drooping of the eyelids, known as ptosis, is a separate issue that can result from various neurological or muscular conditions. Lastly, loss of vision in one eye refers to an entirely different aspect of ocular health, not pertaining to the position or appearance of the eyes themselves. Understanding these distinctions reinforces the definition and implications of exophthalmos in clinical practice.