Author:David Yergoph  From:http://www.aliexpress.com/store/300179  Date:2015/5/28

For PD: (pupil distance, the distance from the centre of left eye to the centre of right eye)
 
How to measure the PD size?
Please visit this link: http://res.ebdcdn.com/video/science/how-to-measure-pd.mp4