Amazingly, they don't! I know, that goes against anything you've heard... but the question is, what does science say? In 1991 they did a research study. Not on screen time, but reading and writing... Do you remember a few years ago? In the 80's and 90's the reason for eye problems used to be reading too much... or reading in the dark... that's why all the "nerds" have glasses... None of that is true! What you read... how long you read... on what device you read... all of that makes no difference... How you hold your body while you read is the important factor! Yes, that's right! The tension in the shoulders and neck cause eye problems. Because they restrict your optic nerve, and the nerves controlling your eye muscles. That's why phones and tablets are worse than computers... When you sit on a proper desk, with a proper computer set-up, you sit mostly straight. Sure, too many people roll in their shoulders forward, but the head is straight. With phones and tablets your head falls forward. You slouch when you look down. That puts a lot of tension on your neck and shoulders. That tension is death for your eyesight... That's also why computer games are so bad. It's not the game, but how you sit to hold this controller... So you have to make sure you keep your neck and shoulders free and flexible... loose, not tightened up! If you are interested, we have a special program/guide to keep your eyes well during the day... And because of that a centerpiece of the Pure Vision Method™ is the whole body gymnastics... is a light and easy healing gymnastics that keeps your neck, shoulders, and back flexible and smooth... Plus, it gets your blood moving, without going to the gym... it's like yoga, tai-chi, and qigong, just without the sweat... Anyways, from now on, watch your posture... especially on tablets! Smart Phones - no matter what anyone tells you, they are not smart... they are convenient! But they are also dangerous for your health if you use them incorrectly... and reading stuff on them is the wrong use... Make good, pro-active use of useful apps... but stop reading, playing, and watching movies on these tiny screens... you'll feel your neck and shoulders lose up right away! Did I tell you? I like your feedback... :) Leave a comment with questions, suggestions, or just to say hi!