I just went through this. I had a dachshund mix that was the happiest dog I've ever known. He was always playing with his stuffed toys, and he loved to go with me everywhere I'd go...he followed my every step at home as well. He was so goofy, and loved it when we'd throw him treats...he'd catch them in the air, it was a game to him.
Last year, when he was 14, I first noticed that he started missing some of the treats I'd throw to him...and eventually he couldn't catch any of them. He also started losing his hearing...he wouldn't react to sounds like he used to do. I took him to our vet, and sure enough, he was losing his sight and hearing. It was amazing how fast it progressed...within a few months, he was completely blind and deaf.
The vet said he would adjust, but he never did. This happy, goofy, lively little guy now moved so slowly, uncertainly, and seemed to be afraid all the time. Riding in the car now scared him, I guess because he couldn't see or hear, and couldn't relate to the motion, and this used to be something he loved. The only time he seemed to be content was when he could be in contact with me...he'd sit leaning against my leg, or lay on his bed if I'd put my foot on it where he could feel it. Once he'd go to sleep, I could move my foot, but if he woke up, he'd whine.
He still ate with good appetite, as long as I'd keep the food bowl in front of him...he'd "lose" his bowl if he took his head out of it, like he didn't have a sense of smell anymore either. I took him out on a leash all the time, and he didn't have any accidents in the house. He didn't lose any weight.
Finally, we decided that he was miserable living like this...I know I would not want to live if I was both blind and deaf. So, we made the decision to put him down. I held him in my arms as he passed, and I literally felt the life leave his body. It broke my heart to let him go, and I've cried many, many times since, to the point that I didn't think I'd have another tear left...and then I cried some more. I'm getting better now, but I still do and always will miss that dog. He was so special to me...my wife has always had dogs, but I've never cared much until I got this one, and he was truly my best buddy. I think every day about him, and I look forward to seeing him again someday...I just can't think that God would give us such a loving creature like a dog, if He didn't also make a place for them to be with us in Heaven.
Let your friend go...it's a kindness. He's not happy, and he deserves a dignified and peaceful end.
R.I.P. Stretch 12/20/13