One of the most frequent questions at the shop when we take out the pupilometer, is “what does that thing do?” Whenever we make prescription lenses for anybody we always use a pupilometer to measure their PD. PD stands for pupil distance, and the measurement is used to center the lenses correctly for the best vision. We love to joke that the pupilometer is a mind reading device, but don’t worry your just getting a New York Pupil Distance measurement from Silver Lining.