It is most probably not your eyes if you already know that they are corrected to 20-15. Have you been checked for cataracts at your age? It may be disturbing to hear, but much more likely that at age 75 your ability to stay focused mentally, not your eyesight ability, per se, is the true culprit here.
It is very common with age to begin to lose the ability to maintain high level focus for longer durations. Here are some tips to help alleviate the effects of this; regarding your pool game :
1. Stay as relaxed mentally as possible during your matches- find whatever works for you to do this.
2. Be sure to have a complete pre shot routine so that your actual final focus on the object ball is kept to the minimum time needed to complete the stroke correctly.
3. Use your time between matches and games to relax yourself, no hyper texting on the phone , stressful personal conversations, etc.
4. Eat lightly before and if you must, during the matches.
5. No alcohol on match day.
6. Get sufficient sleep and rest for a few days and nights prior to your match day.
All of these will help you maintain your maximum ability to focus on match day- being 75 requires much more diligence in these areas to maintain focus over a longer period than when you were 25 - just a fact of life, but you can help with these tips.