Why does grave's disease give you 'bulging eyes'?

See Below: The extraocular muscles and tissue that surround the eye and help it move become thickened and leads to bulging eyes.

Graves Orbitopathy: Some cells in your eye socket share antigens (portions of proteins that immune cells recognize) with thyroid cells. So when your immune system attacks your thyroid, there is cross reaction with tissue in the eye socket, which causes proptosis (bulging eyes), double vision, dryness, swelling, and eyelid retraction, and uncommonly vision loss. This is from inflammation, and scarring in the orbit.