These muscles are triggered by the 7th cranial nerve, which exits the brain in the bony crevice just below the earlobe, and then spreads out across the face.
Although commonly thought to be due to stress or caffeine, in actuality it is merely an irritation to the 7th nerve that is the root cause, in some cases made worse by symptoms of dry eye.
When mild, symptoms can be improved by squeezing the eyelids tightly shut or massaging over the temple. If persistent, changing your pillow can help resolve the symptoms after a week or two by lessening the uneven pressure and nerve irritation that can occur from an old pillow.
If severe, injection of botulinum toxin by an ophthalmologist into the spasming muscles can dramatically lessen symptoms for a few months. And in rare cases of the nerve experiencing pressure from an adjacent artery, a surgical spacer can be inserted.