We all know how when you stare at your iPhone or Blackberry for too long, your eyes start to strain and your head starts to hurt.
Scientists have figured out why, and it has to do with our eyes' inability to focus on a smartphone's small screen AND adjust to how far away the content is from our eyes.
The study, published in the Journal of Vision, shows that this problem could lead to the visual discomfort, headaches and fatigue that come from staring at a small screen or stereo 3D device for too long.
"When watching stereo 3D displays, the eyes must focus -- that is, accommodate -- to the distance of the screen because that's where the light comes from," study researcher Martin S. Banks, professor of optometry and vision science at the University of California, Berkeley, said in a statement. "At the same time, the eyes must converge to the distance of the stereo content, which may be in front of or behind the screen."
Banks and his colleagues had 24 adults look at objects placed in front of a screen or behind a screen. They found that for short distances, the adults felt more uncomfortable when they looked at objects placed in front of the screen, while at long distances, they felt more uncomfortable looking at objects placed behind a screen.
Another study, published in the journal Optometry and Vision Science, shows that people's eyes have to work harder to read tiny text on a smartphone screen because they have to point in the right direction at the same time, USA Today reported.
The researcher for that study, SUNY College of Optometry professor Dr. Mark Rosenfield, said that he came up with the idea for his study by noticing people on the train who held their phones right in front of their eyes in order to read the screens, ABC News reported.
To avoid this sort of eye strain, Rosenfield suggested on ABC News looking into the distance every once in awhile to allow the eyes to relax.