Found this with search phrase "cognitive dysfunction in dogs" (but no quotes). Likely you can find much more.

http://pets.webmd.com/dogs/cognitive-dysfunction-syndrome-dogs

Further, how about talking to the vet again?

Here is a link that might be useful: cognitive dysfunction in dogs

Please see if she may be losing her hearing as well. I had a little llhasa who lost his hearing first, and then the sight in his one eye. He acted like a bumper car for a while, and did a lot of exploring when he took a wrong turn and got lost. If she has had an onset of deafness, then she has lost her primary 'markers' since the loss of her vision and she has scent and vibrations left. And yes, dogs can have onset of what amounts to dementia, ofttimes from cerebral vascular accidents or neurological issues.

I had a dog who developed CCD (canine cognitive dysfunction) in her last year or two of life. It was very disconcerting for both of us. She was frequently anxious, and she was constantly getting "stuck" behind furniture or in corners. Her vision was adequate, but she was functionally deaf. Even so, she couldn't find her way out of a corner or from behind furniture, and she seemed to seek out those locations. I also had to watch her very carefully outside, because she would just start walking very purposefully down the driveway for no apparent reason. She once got 1/2 mile down the road before I realized she was gone. When my SO caught up to her, she was still walking like she had somewhere to go - where, I have no idea.

Although I never pursued it with Sarah, I believe there is medication that can help with CCD. This is something you should discuss with your vet.

Laurie

I went thru this with a dog and it's disheartening to say the least.

I think it's worth checking to see if your dog has a ruptured ear drum. The dog usually has to be sedated for a vet to check for this, so I don't think it'll be seen in a general exam.

I wish I had known about it when my dog was showing similar symptoms..........

Here is a link that might be useful: Perforated ear drum

I also got an email from a company who sends me animal health newsletters. Ironically, this one was speaking about cognitive disorders so I am forwarding the link, in case you want to read it. My older schnauzer was having similar problems but presented with balance issues and he was found to have vestibular issues of the ear and thankfullly when I questioned my vet about that possibility, he concurred and they resolved. Here's the link and no it's not spam.

Here is a link that might be useful: cognitive disorder canine