There are two types of pupil distance (PD). There's a distance PD which is what we need and a near PD. Pupil distance is always written in millimeters (mm) and the larger number is always your distance PD. Now, it can be written two ways. Monocular or Binocular. When a PD is taken monocularly you will see a reading of about 25-35mm for each eye. If taken binocularly you will see something like 55-75mm total PD.