These are the muscles that control eye movement. Eye muscles insert onto the sides of the eyeball and contract (shorten) to rotate the eye in different directions. Any problem with these extraocular muscles (such as a cranial nerve palsy) can make the eyes go out of alignment and cause double vision (diplopia). With strabismus surgery (surgery to straighten the eyes out) the extraocular muscles can be strengthened or weakened by shortening these muscles or by changing their insertion point on the eyeball. Medical conditions like Graves’ disease and myasthenia gravis can also affect the function of the extraocular muscles and cause double vision.