Just on the surface, it doesn't appear that you take much in the way of B6 as a supplement. B6 is stored for short periods of time in muscles. People working out therefore have a higher need for it than sedentary types.

May I ask what is the brand and type of Magnesium you are using?Is it Oxide?

Twitching muscles can be due to imbalance calcium/magnesium.
They also occur during low blood sugar times. These are the two most common causes.

Did you have an A1C done on your blood? Fasting glucose?

You are quite thin for a 6 footer. If you are working out you need a good source of protein. Not everyone does well on a vegan type diet. Type O can have problems with gluten. And also need meats of some type. Type B's also need protein and some dairy too. Type A's do the best on vegetable based diets. (these are blood types). The research on this comes from Eat Right 4 Your Type by
http://www.dadamo.com/

There is a magnesium based lotion now for topical use. It is called Morton epsom lotion. It is rather new and not in all stores yet. You can find it at WalMart, Walgreen's and online at Amazon.
Apply it to twitching muscles and if it stops them quickly, or prevents them, used daily, then your answer is probably magnesium shortage. Your migraine history suggests that too. You don't slather this on, but use small amounts where you need it. That bottle should last a long time...2-3 months with daily use.

Read the reviews here: (many of us on NT now use this lotion. It is really extremely good and very helpful).

http://www.amazon.com/Morton-Epsom-L.../dp/B008X365AU

I think it is best to make changes, and introduce new supplements slowly... one at a time to see what is working and what is not.

I am concerned about the retina issue. I'll have to think about this. If you can get a homocysteine test. If this is elevated it illustrates a problem with methylation of B12, and folate. Elevated homocysteine can affect the blood vessels in the eye..often showing up first there. Your B12 should be the methylcobalamin type, and also folate as methylfolate. Many people have the hidden MTHFR mutation which is a serious health issue for the blood vessels and other parts of the body.

Do you take acid blocking drugs? statins for cholesterol? Did you have thyroid tests?

Sometimes I have to think about things, so if you can.. post again and maybe as a new thread...since we will most likely get offtopic on the B6 issue.
You are welcome to come to our PN forum... we have lots of people with various types of PN and also who follow various diets for various reasons.

http://neurotalk.psychcentral.com/forum20.html
This is the link. There is a subforum there as well with mostly informational posts.

Hope to see you there.