We had a wonderful schnauzer, named Lucky, who lived to be almost fifteen. Toward the end he was deaf, and had cataracts in both eyes, but he was otherwise healthy. He functioned well around the house, and even managed to learn to live in a new home in Florida when we retired. He loved to be outside to enjoy the sunshine, and would locate where the pool edge was by smelling for the chlorine. We finally had to help him to the rainbow bridge when he acquired dementia, and began falling into the pool. At that point he was unable to really participate in family life, and our fear of having him leave us by drowning if left unsupervised for even a minute, made us have that "hard conversation" with our vet.
Our little 5 pound poodle, Beau, is nearly 13 now and has developed a cataract which limits his sight. He is also going deaf. Once again, we are forced to face the fact that his time is limited...but we help him enjoy each and every day to the fullest level that he can. He still has the energy to play like a madman for a few days a week, then sleep for days after! We are not to that point yet, and it sounds like you are not either. My only advice is that you will know when it is time, and do not make him linger because you will miss and grieve him. Our beloved companions deserve to have a loving and kind release.
