If you put the computer on its side you may want to reformat your hard drive after putting it in a vertical orientation. If you also have to see printed material it should be put on a holder next to the screen so it's at the same distance as the monitor screen. In many offices the air is dry due to air conditioning and heaters. To make it worse when we stare at a computer our rate of blinking reduces allowing the eye to become dry. Lubricant eye drops often help.
Electrostatic attraction attracts dust to the screen and eventually hinders visibility.
Clean the screen often. A flickering screen also strains the eyes. Sometimes screen flicker can be reduced by plugging other appliances and lights in different outlets to prevent electronic interference. Also, make sure all your electrical cable connections are tight. Every once in a while readjust your monitors brightness and contrast.