Parents have two more items to add to their back-to-school checklist: an eye check for their children and a review of their computer workstation for possible causes of eye strain.

One out of two children spends more than four hours a day in front of a computer screen, according to the American Optometric Association. But, the association adds, only 16 percent of adults worry that their children's eyes may be affected by such extended computer time.

The association warns that many children may be developing computer vision syndrome due to prolonged computer use.

"Computer use is an increasing source of vision problems, and children may experience many of the same symptoms as adults. Too much time in front of a computer screen can lead to eye discomfort, fatigue, blurred vision and headaches," optometrist Leonard Press, a vision-learning specialist with the AOA, said in a prepared statement. "However, some unique aspects of how children use computers may make them even more susceptible than adults to these problems."

According to the association, parents should be aware that an adult computer workstation may not be suited to a child, who may have to look up at a higher angle than an adult. Parents should invest in a chair that can be adjusted for the child's height. The recommended distance between the monitor and the eye for children is between 18 and 28 inches.

Children may work or play on a computer with a lot of glare for a long period of time without turning down the lights in the room to reduce the glare. Parents can check for sources of glare by sitting in front of the computer. Windows or other light sources should not be directly visible when sitting in front of the monitor. Holding a small mirror flat against the screen can help pinpoint light sources that are reflecting from above or behind.

At the same time, kids' eyes may lose the ability to focus on other objects because of extended computer time. The association recommends that children take at least a 20-second break for every 20 minutes of computer time.

The association recommends that parents take their children for an annual eye exam and discuss computer use with their eye doctor. According to the College of Optometrists in Vision Development, almost one in four school-age children has vision problems, but only 14 percent of children entering first grade have an eye exam.

The association also recommends that parents and teachers keep their eyes open for signs of eye strain in children, including eye redness, rubbing their eyes, head turns, complaints of blurriness or eye fatigue, or limited attention to visual tasks. Data provided by the association indicates that nearly half of parents don't realize that behavioral problems can be a sign of impaired vision.