What is meant by "inter-pupillary distance"?

The term "inter-pupillary distance" refers specifically to the distance measured between the centers of the pupils of the eyes. This measurement is crucial in optometry and optical fitting, as it helps ensure that optical devices, such as glasses, align properly with the visual axis of the wearer's eyes. An accurate inter-pupillary distance is essential for providing optimal vision correction and comfort when wearing lenses.

When fitting eyewear, taking this measurement allows opticians to position the optical centers of the lenses directly in front of the pupils, minimizing optical distortions and providing clear vision while also enhancing comfort. This is why understanding the specific definition related to the centers of the pupils is vital in the context of optical training and practice.