My eyes have always been sensitive to bright light. I am severely myoptic too. So I wear Eagle Eyes sun glasses driving (over 10 yrs now). And I have transition lenses for everyday brightness.
BluBlockers and Eagle Eye sun glasses change the blue wavelengths of bright light, and help with focus. The blue in bright light may not focus completely on the retina due to its wavelength and cause a blur result. BluBlockers tend to make things orange, but the Eagle Eyes do not. Both my hubby and I use one or the other driving, and they make it much less tiring. They also work well on foggy overcast situations.
http://www.eagleeyes.com/technology/lens.lasso
They are pricey but very very good. I think you might like them.
(Amazon has them less $$ than the website)

One can have optic neuritis associated with low B12 levels, too.

It might be a good idea to use the special formulas made for vision. Like Preservision vitamins. They contain antioxidants and zinc.

Since you've already been to the doctor about this, all you can do is try the supplements for the retina and sunglasses.

I have severe light sensitivity. I keep my blinds closed and have black out shades for one room.
I have a lot of eye problems so have seen many eye specialists. Then when things were ruled out after many tests I went back to my neurologist who did an mri. Are you under the care of a neuro? Maybe you could talk to him or her about that. Do you get any head aches or pressure in your eyes or near?