The risks of smartphones go far beyond thumbs, wrists and sanity: A new study finds that the devices might be doing a
number on your eyes, too.

iPhones, BlackBerries and Androids help millions to work, keep in touch and stay entertained all day and night -- but they're also responsible for some pretty bad habits.

And it starts with how we hold them.

Researchers asked 130 volunteers with an average age of 23 to read text messages on their smartphones, then measured
the distance between their eyes and the screen.

And as it turns out, the volunteers almost all held their phones much closer than they would a newspaper, book or magazine.

The researchers say the text readers held the phone about 14 inches away, with some holding it as close as 7 inches --
compared to an average of 16 inches for normal printed materials.

In a similar experiment, 100 participants with an average age of nearly 25 were asked to read a Web page on their smartphones -- and researchers say they held the phone just 12.6 inches away.

So do those extra inches make a difference? You bet they do -- the researchers say it could place an extra strain on the
eyes, especially for people who already wear glasses and contact lenses.

They even suggest that optometrists consider testing vision at closer ranges for some patients and alter prescriptions
based on mobile viewing habits.

Since Web-based text tends to be smaller than newspaper print -- in some cases up to 70 percent smaller -- the most
immediate action you can take right now is to go into your phone's settings and adjust the font size.

Another option is to switch to a larger device for more serious reading -- including the Kindle and tablet computers like the iPad. In addition to larger screens, these devices contain even more settings to allow you to adjust text size as well as brightness.

Finally, keep in mind that it's OK to put these devices down and even turn them off every now and then.

Sometimes, the eyes just need a rest no matter what you're looking at.