For a while I thought it was caused by eye strain, but then I got glasses for reading and computer work and they didn't help. At all. Very sad.
So I've been trying other stuff ... medication, acupuncture, more medication, relaxation, uh, I think that's it.
Anyway I still think it might be eye strain, and if it is, I am totally getting a sweet pair of glasses on Etsy! Here are some I'm considering:
Clockwise from top left: