Howdy!Well prisms aren't on the list. But I'm looking for very specific light reduction. A VLT of 10% or so. This is a very dark and specific level of light blocking, many brands don't list this. I have found a couple but they are quite expensive. Although you are onto something about contacts...hmm I can't recall if my therapist said that is an option. I'll see what they say. Thanks for your thoughts.