This app is good for your eyes.
If you or your little ones are using the iPad continuously for more than 20 minutes, you need eyes rest. Just a few seconds looking far will do the trick but you need to be reminded when to do it. Even better. You may want to track the time of iPad usage to become more aware of your reading habits and their relation with eye strain. Finally, if you feel that your experience can help others, you can share your data and insights with scientists working in vision research.
The app is free.