Measuring Pupil Distance (PD) for ordering Glasses Online.

Pupil distance (PD) is one of the measurements that are required for ordering glasses online.  Pupil distance is the measurement in millimeters between the center of the pupil (black circle in the center of your eye) in each eye.  Pupil distance can be either monocular or binocular.  Monocular means the distance from the centre of one pupil to middle of your nose bridge.  While binocular is the distance between the pupil center in each eye.

To measure pupil distance you need a person facing you at your eye level.  Therefore if you are a tall person you may need to sit down to be eye level.  The person facing you needs to place a rule with millimeter graduations against your forehead with the 0 at the outer edge of your pupil (one nearest your ear) to the inner edge of the pupil in the other eye (one nearest your nose).  If you require monocular measurements the person facing you need to place the start of the rule graduations level with the centre of your pupil and measure to the center of your nose.  This needs to be repeated for the other eye.