Probably a few. Surgeons have the same spectrum of illnesses that the general population suffers. That includes diminution of eyesight with aging and other sources. Most recognize this deficiency and get it fixed or cease surgery if that is not possible. But i would guess there are a few who deny their handicap in this arena (just like car drivers who cannot see well), and thus can be a problem.
Sure. We age the same way everyone does. Interestingly, there are no fitness exams for surgeons to pass the same way, for example, pilots have to. We do rely on self reporting for incapacity, as we all take our privilege of caring for patients very seriously.