Mirror Mode

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In general, the test distance has better to be at least 2 meters for early detection of short-sightedness or myopia. With the mirror mode, you can stand in front of a mirror, with your eyes around 1 meter away from the mirror, so the test distance is 2 meters. Therefore, it is quite convient to test in a regular residential bath room with a mirror. 

To keep only either eye opened, you may use an eye patch.