I have had both tests. The EEG was looking for seizures, it measures brain waves. The VEP was (from what I was told) to look for damage from Optic Neuritis. That one for me was slightly abnormal and I was not in a flare when it was done.

It is not a direct way to diagnose MS, but there really isn't one. But they are probably trying to find all of the info they can and compile it all together. With all the information of what they have found and what they have ruled out they can possibly confirm the MS.

I hope this helps.