My Moms two sitsers went thru something very similar. They were diagnosed with calilcification of the brain, where your nerves turn to calcium and no longer work. The result is your brain recieves incomplete data and is forced to guess what the eyes are telling them. The eyes send the code that they are seeing a dog, but the missing nerve endings garble the message and what arrives to the brain doesn't make sense so it searches for the closest thing the code is sending- which might be ice cream, television or flying oak trees.
It is truly horrible for the cargivers. It was even worse for my one Aunt as she must have realized she herself was beginning to suffer even as she was the main caregiver. Before the disease, the two of them lived on a cruise ship for almost two years, enjoying their well earned retirement.
My Mom was beginning to show some signs, plus she was legally blind so she was double whammied. Seeing things that weren't there and not seeing things that were.
Mercifully, her heart wore out before her brain. I'm sure she would have wanted it that way.