Computer vision syndrome

Definition
Computer vision syndrome (CVS) is

"a group of eye and vision-related problems that result from prolonged computer use. Its symptoms include headaches, blurred or blurry vision, neck and back pain, redness in the eyes, generalized fatigue, eye strain, dry eyes, irritated eyes, double vision, polyopia, and difficulty refocusing."

Overview
"Computer vision syndrome is caused by our eyes and brain reacting to characters on the screen differently from how they react to characters on a printed page. Human eyes have little problem focusing on most printed material, which is characterized by dense black characters with well-defined edges. Healthy eyes can easily maintain their focus on the printed page. Characters on a computer screen, however, don't have the contrast or well-defined edges described above. Consequently, these characters (pixels) are brightest at the center and diminish in intensity towards the edges. This makes it very difficult for eyes to maintain their focus and remain fixed on these images."