My Doc called them Ocular Migranes and ordered a carotid ultrasound that found a carotid artery about 60% occluded. A couple years of low dose aspirin seemed to reduce the events to about 1 or 2 a month.
"Some people get the visual symptoms without the headache. This is called Ophthalmic Migraine. The cause is due to a temporary spasm in the blood vessels behind the eye called “vasospasm” similar to a spasm or cramp that you may have once experienced in one of your leg muscles (Charlie-Horse). Usually, this resolves without treatment and many people never have another episode. Some people may continue to have them. An examination of the eye is important to rule out any other causes for these symptoms."