I learned to keep my eyes fixed on a corner of a painting or a cushion while meditating. Just keep looking at the same thing, looking carefully, looking steadily. Sometimes, my eyes get tired. I learned in grad school that the eyes get refreshed by blinking. I have read that some computer work tends to keep the worker from blinking resulting in tired eyes. Then, I read that many ancients learned to concentrate on their breathing instead of what they could see. I found that I could concentrate on my breathing with my eyes closed, giving me eye rest instead of eye strain.
I have been suspicious of numerical standards ever since I read the ideas and history of W.E. Deming. Plus, my experience in Quaker meeting showed me that our eyes, our attention, much of our being, is predicated on renewal, new situations, arising dangers and unexpected opportunities. While exploring breath and its uses, I came across "Breath by Breath" by Prof. Larry Rosenberg. That's the book that includes the story of Americans in Korea finding they will be asked to go without sleep for one week. Don't ask me why. Some people, especially male people, need challenges and conquests and wins. Rosenberg's group was advised to just pay attention to the very present, what they were up to, moment by moment, and nothing else.
I have heard of the British expression "working to rule". It is a labor tactic to fight employers and it consists of doing just exactly what is required by contract and nothing more. Paying strict attention to this moment, as is, as I am, quickly changes my world and my feelings. Where are my feet? What do I smell? What do I hear? Gosh, I just took a breath!