It is believed retinal migraines are caused by "vasospasms "of the blood vessels of the eye in the area of the "retina". The retina is at the back of the inside of the eye. In medicine a "spasm" is a sudden constriction or tightening of muscles that is "involuntary" - a person does not control them they move on their own. Muscle spasms can happen in different muscles of the body, like when a person's leg or eye "twitches". The twitching is caused by the spasms.