Your prescription can change (I had 20/20 vision & no reading glasses, until I was 54; four years after that I had trouble seeing and indeed my prescription was

Your prescription can change (I had 20/20 vision & no reading glasses, until I was 54; four years after that I had trouble seeing and indeed my prescription was no longer correct). But why each year? I assume the Opthamologist association would say (as referenced in the article) that they need to look for ocular disease, or diseases that are detectable through eye exam (e.g. diabetes). Not clear to me!