Depends on the cause of the strain:
If you are using a font that is too small, you tend to try to focus. This affects the muscles in your eyes that change the shape of your eyeball.
- Try increasing the screen font size to the next size up.
I find that newer LED monitors are too bright, and too high contrast.
There usually is a button that brings up an on screen menu where you can control brightness and contrast. Try playing with this.
Try a different colour scheme. I do all my file editing in a window using dark blue type on a wheat coloured background.
There is often not enough room light. Whenever you look away from your monitor, your eyes dilate to get more light, then contract again when you look back to the screen.
- Increase room lighting in your normal field of view.
- Dim your screen.
If your monitor sits so that one edge of it is nearer your eyes than the other edge, then your eyes have to constantly shift focus as they move around the screen
- Move your monitor so that the centre of the monitor is at right angles to your line of vision.
If your eyes are used to reading at a distance of 14-16 inches (common position to hold a book or magazine) and your computer monitor is at 24 inches, then you are focusing at the wrong distance for you.
- Try moving your monitors closer to your eyes. Note that many monitors doing this will also mean you are looking down more. Put a phone book or two under your monitor.