Welcome to the forum. You sound like you are in good hands with your doc and its wonderful that he is looking into other things. MS can be hard to diagnose sometimes because there are a lot of different things that share similar symptoms. And to boot, theres not one single test for it but several, a few of which, the MRI and VEP you've already had done. The lumbar puncture is another one, but they usually save that one for last as it's not always necessary.
The nerve problem of the eye your doctor is talking about is called optic neuritis if didn't already know the term and wanted more information on it. The VEP you had done should show if you have it.
Please hang in there, share your frustrations and feelings here if you like. We have a great group of supportive people here who will listen and help you through things. Let us know what your tests show. There are a lot of resources here to look through, check those out and there is a link to a ms mimic website in the resources thread at the top of the MS forum thread list. The National MS Society website has some good information as well and you can find that at http://www.nmss.org
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