Once you’ve found your favourite frame, it’s time to measure your Pupillary Distance (PD), or the distance in millimetres between the centres of your pupils. Knowing your PD helps us craft your lenses to suit your eyes, and makes sure that you’re always looking through the right part of your lenses.
In other words, it’s one extra step to make sure that your new specs are, well, properly specced.
If your glasses aren’t tailored to your PD, they could cause anything from eye strain and poor vision to fatigue and headaches. The higher your prescription, the worse the potential effects of an incorrect PD.