hi,any decent opticians should be able to accommadate your needs,the sunglasses should be uva and uvb protective and also give good clarity in what is called ‘flat light’ (this is when the sun is clouded over and or towards the end of the day as the sun dims,so there are no shadows to show the undulations in the snow,this kind of light makes negotiating different snow conditions slightly more difficult,baring in mind a persons eyesight changes with time a costly pair of sunglasses made especialy for skiing could prove costly in the long run.
But if i was in the market for a good pair of specialy made sunglasses i would contact Vuarnet as they were designed originaly by the french skiing 1962 olympic gold medalist Jean Vuarnet in conjunction with the Pariloux opticians in Paris,i would imagine your friend could obtain a pair to thier eyesight requirements for around £150-£200 or so(this is just my opinion though as i do not where glasses i can only give an estimation for the price as my Vuarnet sunglass were £75 some years ago).
Sorry i annot be of more help.
many regards
jonG.