My first thought is that your snake is probably in shed, although i have no personal experience of only one eye going milky... It should clear again after a few days, then he/she should shed within a couple of weeks. How old is your snake and how long have you had him/her?
:Hi All, :My cornsnake seems to have white glaze over one eye and sort of looks a bit like a cataract. Does anybody have any idea, what this could be and how to deal with it. I can send a photo if it helps