On the home screen of your PDCheck app you will see the following:
PD: Short for Pupillary Distance. This is the distance, measured in millimeters, between the center of your pupils. This value is required in order to make sure your eyes will be looking through the center of the lenses and be able to focus properly. It is important to measure and report this value correctly to the manufacturer of your glasses.
Left and Right PD: These values are the distance from one pupil (either left or right) to the center of your nose bridge. You can either use this value or the combined value above when ordering glasses. For most people, the left and right PD are approximately the same. However, if they are significantly different, we suggest you use these individual values when ordering glasses.
Near PD: This value is used when ordering reading, progressive, or bifocal glasses. When ordering glasses primarily used for near work, you would provide this value to ensure your eyes will be looking through the correct part of the lens for proper focusing.