According to my rabbit vet, cataracts in bunnies are not treatable. One of my bunnies eventually did go blind from them but you never would have known it. He scooted around and was very active anyways.....he had memorized the layout of his room so I couldn't rearrange the furniture! When he died it was age-related and had nothing to do with being blind...

My other thought is that you should probably get your bunny a companion if he doesn't have one already.

Whatever you do though, do NOT take your rabbit who does not specialize in rabbits, that is just asking for real trouble.