Since pupillary distance changes with physical development, a growing child’s measurement will likely change over the years. But once reaching adulthood, very little change in our skull shape takes place, and pupillary distance remains constant.

Is it possible for your PD to change?

Pupillary distance is measured in millimetres, and is sometimes expressed as ‘PD’ on your prescription. Your pupillary distance can change during childhood and adolescence, but will almost certainly remain the same once you reach adulthood.

Does PD need to be exact?

Your PD should be exact. If your lenses aren’t centered correctly, they can cause discomfort and eye strain. A small margin of error might not cause problems, but it’s better to be as accurate as possible.

If the PD measured was 2mm off initially, by using a millimeter rule, the net cumulative error might be 4.5mm or more.