The body is alive and as living tissue it will respond to become better at what is asked. If this is not the paradigm that you are trained to see the body, it might take some practice. For instance, sometimes you hear people recommend that drinking lots of water directly before or even with your meals to provide you a full feeling and help you eat less. But there are those who say that this water would dilute the acid in your stomach and, thus, make your digestion less efficient, and the body's response to this would be to increase acid production of the stomach. Seems simple, yet without such a perspective we might be tempted to take something like an antacid to deal with the increased acid and this would further limit the acid effectiveness, and perhaps stimulate even greater production of acid. In this scenario it is easy to see how a mechanistic controlling approach to the body might cause a negative cycle that would not occur with an approach of working with the body.
Changing your view of your body and understanding how it is trying to become better at what you want - based upon what you do - can have a significant shift in how your body responds to your concerted efforts. Certainly there are limits to the body's ability to adapt, but with a greater understanding of how the body is actively and continually adapting we can have greater control over the direction of the adaptation. For the greatest range of ability it is important to have the greatest variation of activities. For your eyes that means you need to give the close focus a break by focusing on some distance. Finding the right balance can be hard, but realizing the power you have to make a difference is a great start.
As always, let me know how I can help.