Parallel with the belief that vision will fail, you may have the before-mentioned belief that hearing will dim, ad these two ideas may be reinforced by a belief that age automatically makes you less a person, turning you into an individual who can no longer relate in the daily pattern of environment. The belief, you see, would work to insure the materialization of that state.
On the other hand, you may believe that wisdom grows with age, that self understanding brings a peace of mind not earlier known, that the keen mind is actually far better able to assess the environment and that the physical senses are much more appreciative of all stimuli.
And so those conditions will be physically met in your experience. THe physical apparatus itself, following your beliefs, will continue in health.
You must understand, again, that your ideas and thoughts do not exist as phantoms or shadow images without substance. They are electromagnetic realities. They affect your physical being and they are automatically translated by your nervous system into the stuff of your flesh and of your experience.