> the trick is shifting focus from farther away back to close Hence the 20:20:20 guideline that says after 20 mins of near work, one should spend at least 20 s

> the trick is shifting focus from farther away back to close Hence the 20:20:20 guideline that says after 20 mins of near work, one should spend at least 20 seconds looking at an object 20 feet away. The same principle applies to extended contraction of your arm, core, eye or other muscles. https://en.wikipedia.org/wiki/Spasm_of_accommodation https://en.wikipedia.org/wiki/Spasm_of_accommodation