Hi Des, does that strange kind of Optic Neu.. happen to MS peoble? I´ve not heard of that before, if it does, I would not rule MS out just because it does not show on the MRI jet. I would see a neuro, he could check if you have pinched nerve or something else. Ofcourse there are also so many ms mimics out there, so that could be so many things. I hope you get this figured out soon, but more often it takes a lot of time (my experience, I´m not diagnosed yet, after two years waiting). Good luck!
The most common cause of such insensitivity is diabetic neuropathy, so before worrying about MS, schedule a simple inexpensive Hba1c test. That being said nerve compression (or a neurological disorder) is also a possibility, and a 3T MRI of the ankle would be helpful, as well as an EMG. The 3T (in contrast to the 1T) provides a clearer image of the small nerve sheaths.
You should consult a Neurologist.
Any imaging done yet?
Does sound suspicious of a pinched nerve.