Real Simple answers your questions.
Q. Is reading on an e-reader bad for my eyes?
A. Not in moderation. So says Harvey Moscot, a New York City–based optometrist. That said, if you spend a long period (more than two hours) staring at a screen—on an e-book, a smart phone, or a laptop—you could suffer from what is sometimes called computer vision syndrome (CVS), a repetitive-stress condition characterized by some uncomfortable side effects, including headaches, blurred vision, and eyestrain.
To prevent CVS, some e-readers, like Amazon’s Kindle, use “electronic ink,” which has sharply defined type and is easy on the eyes. Reading on electronic-ink devices compares most closely to doing so on paper (which is what our eyes tolerate best). Other e-book models, like Apple’s iPad and Barnes & Noble’s Nook-Color, have a backlit LCD screen, similar to a computer monitor. Even though these devices generate their own light, you may want to keep a lamp on close by (no reading under the covers!). A stark contrast between the screen and your surroundings is hard on the eyes.
Also take brief breaks to avoid eye-strain, says Moscot, who recommends the 20-20-20 rule: After 20 minutes of reading, focus on an object 20 feet away for 20 seconds.