What causes someone's eyes to bulge out?

Different things : Some people naturally look that way, thyroid disorder can do it. A tumor behind an eye can push it forward, as might blood in the orbit. If you notice a change from previous photos for instance, you may want to see an eye doctor who can use a hertel to measure the amount of "proptosis.".

Something behind eye: If your eyes are bulging there could be something behind the eyes causing it. Most common is related to your thyroid but it will need to be evaluated by an ophthalmologist.