Eyestrain associated with computer use, or even prolonged reading and desk work, can be caused by 2 major factors: Eye muscle pain and dry eyes.
Eyestrain during prolonged and visually demanding computer work taxes the orbicularis oculi muscle. It’s like doing physical labor for a prolonged period. When you use the same eye muscles for hours, even half an hour, your eyes get tired. There is increased blood flow to the muscles 6 extra-ocular muscles around your eyes. These muscles are “exercising” as they precisely coordinate and move the eyes across thousands of words and lines of print. Simultaneously, the accomodative muscles must focus very rapidly to fill in the gaps so that the rapidly flickering screen appears stable, even though an electron beam is sweeping across the computer screen to refresh the pixels to form words and images.
It is easier on the eyes to read printed matter, or even a Kindle type device, because the print is stable, and not flickering.
The eyes also dry out more while working on the computer because blink rate slows down to minimize disruption of the image to the brain. The less you blink. the less interruption to your concentration, and therefore comprehension and processing of what you are doing. Beware of using over-the-counter artificial tears that only replace tears. Your eyes tend to feel good for 15-20 minutes, then more dry and sticky after the artificial tears drain out of your eyes. I recommend homeopathic drops that not only replace tears, but also stimulate tear production.
Take visual breaks every 20 minutes to decrease eye strain, make sure you are wearing a prescription that is less than a year old to correct for astigmatism and refractive or optical problems, and use homeopathic tear drops to stimulate tear production.