Litter Box Issues

Dear Bunny Moms and Dads,
My 6 year old Holland Lop bunny suddenly went blind last summer (over the course of two weeks). After countless vet visits and tests, it was determined that cataracts was NOT due to Encephalitozoon Cuniculi. Two vet ophthalmologists I was refereed to did not impress me at all: both of them had no experience dealing with rabbits' cataracts. So, we left it as it is, just like our primary vet suggested.
Now, my buddy is completely blind; HOWEVER, it doesn't stop him from living his life: he eats, he drinks, gives bunny kisses, etc.
About two weeks ago, he completely stopped using his litter box. I haven't changed its location, the type of litter, etc. He does seem to drink a little more than usual but, hey, it's summer!
Has anyone experienced something similar with their rabbits? Can he just be too blind to find his litter box?
Right now I have a stinky bunny. We end up washing his butt every evening because urine odor is unbearable. I mean, he doesn't even move out of a puddle, he just sits in it!!! I tried using wee-wee pads but he rips it into little pieces.
I bought diapers for premature babies that seem to fit him but I decided to share this post here first. Do you think it's OK to use diapers on disabled bunnies? (I have encountered mixed opinions when doing my online research.)
Can this litter box rebellion be a sign of a serious health issue like UTI or bladder stones?
Any feedback is greatly appreciated!!!

The litter box issues could be a sign of a health problem. A UTI, stones, or calcium build up in the bladder are possibilities, but so is e. cuniculi and even arthritis/spinal issues. It would take another vet visit and diagnostics to figure out if it's a health problem causing the change of litter habits.
http://www.bio.miami.edu/hare/urinary.html
http://wildpro.twycrosszoo.org/S/00dis/Miscellaneous/UrineScaldingRabbit.htm

Or the loss of litter habits could just be due to his loss of sight and he's decided it's too much trouble to make it to the litter box. There are people that have used diapers for disabled rabbits, but it does possess some possible complications such as if the rabbit starts chewing at it, as well as the fact they won't be able to get to and eat their cecals. This link about caring for disabled rabbits, might have some useful tips for you.
http://www.disabledrabbits.com/

I was able to use disposable pee pads for my disabled rabbit, but that doesn't seem like an option that will work for your bun. Something that might work is to use disposable pee pads underneath vet bed type fleece, if you don't have too large of an area to cover. It will provide a soft layer that is washable, helps drain the urine away from your rabbit to the disposable pads underneath that can be changed out as needed, and your bun won't be able to get to the pee pads to rip them up. I had part of my rabbits area set up like that, but just a smaller area as she wasn't very mobile.

If you haven't already had your rabbits bottom fur clipped, that would probably make things a bit easier if the urinary issue isn't due to a health problem that can be resolved, and is something you'll want to have done if you decide to go the route of using diapers.

I had a rabbit who was deaf and then went blind (her case was E. cuniculi) and she still used her litterbox ok. I agree with Jbun- start with a vet visit about the sudden change in behavior- I'd be thinking UTI/calculi type of thing. Also, although he's a bit young for it, it could be arthritis or something, so that it's hard to jump into the box.