Darken your screen
Those are not just letters and numbers on your screen, they are also tiny light bulbs that send light directly into your eyes. You need to turn the wattage down, so to speak. Do not make the letters too bright. Turn the brightness down to a dim level and then adjust the contrast to make up the difference. An added tip. Take a pencil and make a mark on the knob you adjusted. Then make a corresponding mark on the computer. That way you will just have to realign the marks if somebody changes the setting on your computer when you are not there.

Work in the shade
When it comes to relieving eyestrain, it is best to keep your computer in the dark. Shade your screen by creating a hood over it. Go to an art supply store and buy a sheet of heavy black cardboard. Put it on top of your terminal and fold both sides down over it. That will llow you to slide it back and forth What you have done essentially, is put your machine in a black box. So now you can turn the brightness down to a very low level.

Shut out the light by shutting your eyes.
The best way to relieve eyestrain is to rest your eyes. And that is easier than you might think. You can do it while you are on the phone. If you do not need to read or write, just close your eyes while you are talking. Depending on how much time you spend on the phone each day, you may be able to rest your eyes for almost an hour or two daily, people who practice this technique say their eyes really feel better, and it helps rid them of eyestrain.