Pupillary distance

[1] Distance PD is the separation between the visual axes of the eyes in their primary position, as the subject fixates on an infinitely distant object.

[2] Near PD is the separation between the visual axes of the eyes, at the plane of the spectacle lenses, as the subject fixates on a near object at the intended working distance.

[4][5] For people who need to wear prescription glasses, consideration of monocular PD measurement by an optician helps to ensure that the lenses will be located in the optimum position.

[7] These viewing systems include binocular microscopes, night vision devices or goggles (NVGs), and head-mounted displays (HMDs).

[19] These devices can be designed to fit a large range of IPDs as factors such as size and weight of the adjusting mechanism are not overly critical.

In contrast to microscopes, the weight and bulk of night vision goggles (NVGs) and helmet-mounted displays (HMDs) are large factors for wearing comfort and usability.

The fixed-IPD design strategy assumes that the exit pupil will be large enough to capture the IPD range of a targeted population.

[23] These databases express the IPD for each gender and sample size as the mean and standard deviation, minimum and maximum, and percentiles (e.g., 5th and 95th; 1st and 99th, 50th or median).

[citation needed] Several binocular HMDs that support night vision position the sensors on the sides of the helmet, effectively extending the IPD by approximately 4x and creating hyperstereopsis.