I'm so sorry to hear your news. My mum (who now lives alone) has just had to have her 16 year old cat put to sleep. She went off her food and became very disorientated. She started hiding behind the tv amongst all the tv wires. It was really distressing to watch. My mum took her to the vets where they said she had cancer in her tummy and also her eye, she was totally blind. The vet did give her a massive dose of antibiotics which helped her improve for a few days, but then she declined again very rapidly. So I'm afraid the vet put her to sleep. I feel for you but I'm sure your dog had a happy life, as did my mum's cat.