A
major nuisance. The usual sort of
migraine, the one that gives everyone
headaches, is caused when a
blood vessel somewhere in your
brain pinches shut and causes an uncomfortable sort of
feedback.
Ocular migraines are just like that, except the blood vessel is in your
retina. It causes weird, vibrating
psychedelic patterns to take up part of your
vision for several minutes and, sometimes, gives you an
annoying headache to go along with it.
I'm having one right now. It makes it rather difficult to read what I'm typing. Not to mention the headache.