As far as I know there has been no found relationship between migrains and diabetes. If you're glucose intolerant, I'm sure your doctor has instructed you on proper diet and exercise and all that in order to counter it. "Optical" migraines are a real, documented thing. Lots of people get what is referred to as a "migraine" but the manifestations are different in almost every person. I'm not exactly sure what specifically happens in a migraine, and I'm not sure anyone really does in the medical world, but it has somthing to do with the nerves in your brain firing abnormally, usually starting at the back of your head and moving forward (this is how the firing goes, not necessarilly the pain or other manifestations). If they are bothersome, your doctor should be putting you on a class of drugs known as the "triptans". Some of these include Imitrex, Maxxalt, and probablymost of the migraine drugs you see advertised on TV. They've been proven to help a lot of people, and if you're not on one of these, I'd reccomend you talk to your doctor about it. If you are on something, just call your pharmacy and ask the pharmacist if the medicine you take is a "triptan", or feel free to post the name here and I can tell you as well
If you're really aching to know more about migraines, I can try and pull out some of my old notes from pathophysiology and give you some more info.