Do you ever notice that after a couple of hours sitting at the computer you don't feel very well? It could be a condition called Computer Vision Syndrome.

Will Bulka spends a big chunk of his work day online.

"I look at a computer screen anywhere between 8 to 10 hours a day," he says.

It takes its toll. He says, "You know, I come home from work sometimes with terrible headaches."

Headaches, blurred vision, focusing problems: All symptoms of something practitioners refer to as Computer Vision Syndrome. The American Optometric Association says CVS is not an official diagnosis, but is a real problem. It impacts as many as 70% of those who work on their computers daily for at least two hours.

Dr. Jim Sheedy is with the American Optometric Association. "It's just proliferated as computers have proliferated in our workplaces and our homes," Dr. Sheedy says.

It can also happen when you're texting a lot.

It can affect anyone but certain groups are more prone to problems. "Anyone who requires bifocals or progressive lenses to work at a computer, because your typical bifocals are designed for looking down about 25 degrees at a viewing distance of about 16 inches. That's not where the computer is so very often a person needs to take their general issue bifocals and go like this and then like this and they end up with neck and back aches," Dr. Sheedy explains.

It could also cause dry eyes.

"Their blink rate goes way down. They only blink about one third as frequently as, say, when you're engaged in conversation and the primary reason is to re-wet the eyes. So if your blink rate goes down, your eyes are open longer and you tend to get dry eyes," Dr. Sheedy says.

Postmenopausal women are also at risk because they may have dry eyes to begin with, and anyone at any age who plays computer games for hours is also vulnerable.

What can you do? Fix your work environment for one.

"You should not have bright peripheral lights in your field of view and get your computer display straight in front of you. You should not have to look off to the side to see your computer display. Also, the display should be at the same horizontal level as your eyes and this way you're looking slightly downward at it," Dr. Sheedy suggests.

And use the 20-20-20 rule, taking breaks every 20 minutes for 20 seconds, looking off about 20 feet at something three-dimensional instead of flat.

That helps Will Bulka. "I'll go walk outside, try to get some sunshine just get my eyes where they don't have to focus so much on a, on a gleaming screen," Will says.

Dr. Sheedy with the AOA says the good news is that there's no real evidence of long term damage from CVS, and that if you're suffering there is treatment.