Blind cat now spraying

My 17 year old cat Duke went totally blind about 4 weeks ago for reasons unknown. He was already blind in one eye before this. I called the vet's office and was advised that all that could be done was to take him to a specialist 150 miles away. Due to his age, I decided not to take him and put him through all the stress. Other than the blindness, he is in good health for his age.
He is doing quite well. He knows where his litter box is and his food and water. He has been jumping up in my lap to get petted and purrs a lot. He has even jumped up in the window and I found him one day sleeping at the top of the stairs like he used to do.
But I caught him twice in the last 4 weeks spraying. Once was against the front door and today it was on my shoes. It is definitely spraying and not just peeing. Any ideas why he is doing this and what can be done about it? Thanks.

I m so glad he is doing as well as he is.

But, the spraying could be indication of urinary problems. A vet visit is definately in order. A significant change in an animals demeanor is always a cause for concern.

If the vet can't find anything urinary wise, the spraying could simply be due to the fact that the cat is now completely blind. He could be attempting to mark his territory as a way to control the environment - making it smell very familiar (which your shoes and the various smells coming in the front door wouldn't be).

I suggest putting shoes up. He won't see shoes anymore, he'll just know there's a bunch of different smells in one small area. Who knows what a cat could think that is?
Try feliway diffusers.

But sudden blindness in itself is serious. He could be having blood pressure issues, which can kill him. He does need to see a vet concerning the symptom of blindness.