Eye Defender is a simple app intended to help you prevent eyestrain.
It's job is simple, after some period of time it reminds you to give your eyes a break. After that you can continue your work.
In Screen-on protection, you will be notified to rest your eyes after you have used the device for the selected period of time.
In Screen-off protection, counting will start after you turn off your device's screen. This mode is intended while reading or working on a computer and you don't use your device.
If you have enabled both protections, you will be notified regardless of the screen state. It is assumed you switch from activities simultaneously, without making a break.