PD is your pupillary distance – the distance between your pupils in millimetres. We need your PD so that the centre of each lens sits in the right place in front of your eye.
Your PD can be:
- One number (for example 64) – the total distance between your two pupils
- Two numbers (for example 31/33) – a separate measurement for each eye, taken from the middle of your nose. This is more exact and is actually the better option.
A normal adult PD is usually around 54–74 mm. PD doesn't change in adults, so even an old PD value is reliable.