Rest the eyes at intervals. Look into the distance, this decreases the eyestrain. Change of focus relaxes the strained eye muscles.

Blink your eyes consciously intermittently. What happens is, you keep on staring at the screen with concentration, without blinking. This causes drying of eyes and leads to redness, eye pain. Artificial tear drops may be needed.

Get your eyes checked from an experienced Eye Care professional. Convey your problem. Correct any refractive error. All these years, there was a need only for distance and near correction. Computers have created a need for refractive correction at intermittent distance. Trifocal Glasses may be required. 

The light reflection from the computer especially added with improper room lighting, glare from other light sources while working with the computers can cause eye strain. Many now recommend a special coating on Eye glasses to decrease these reflections from the computer. 

Positioning of the computer is important too. The screen should be at eye level, with the top of the computer just visible while sitting erect.