I have just reinstalled the old too-small used-twice-and-botched Fresnel (plastic temporary prism) on my glasses at 45º because the one that was installed (horizontally) was not working any more. I had been noticing that my double vision was now at 45º (originally vertical, horizontal at the last eye clinic visit and due to the MS, apparently, which is why it keeps changing). This fluctuation means that I cannot have glasses with a permanent prism and so I will have to cope with this feeling of looking through a bottle bottom with vaseline smeared on it that these damned fresnels cause so that I can see one of everything instead of two.
I had wondered why my right eye was hurting so much for the last three days and then I remembered the last time that this happened and decided to play with the old fresnel. I am s glad that I had kept it!