Pupillary distance
Encyclopedia
Pupillary Distance or interpupillary distance
(IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupil
s in each eye. This measurement is used when preparing to make prescription eyeglasses. Positioning lenses
correctly in relation to the centre of the pupils is especially important for higher powered lenses due to the location of the optical centre of the lenses. It can also be relevant to binoculars
: they must be adjusted to suit the user's IPD; and the minimum allowed by some binoculars is still too great for people with a small IPD.
In very young children and babies, where the patient is unlikely to stay still, the optical professional will typically measure from one medial canthus
to the other lateral canthus.
In the UK, the PD measurement is classed as a dispensing tool rather than a part of the actual prescription of the person whose eyes were tested, thus there is no obligation for a PD to be provided on patient request.
Interpupillary distance
Interpupillary distance is the distance between the center of the pupils of the two eyes. IPD is critical for the design of binocular viewing systems, where both eye pupils need to be positioned within the exit pupils of the viewing system. These viewing systems include binocular microscopes,...
(IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s in each eye. This measurement is used when preparing to make prescription eyeglasses. Positioning lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
correctly in relation to the centre of the pupils is especially important for higher powered lenses due to the location of the optical centre of the lenses. It can also be relevant to binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
: they must be adjusted to suit the user's IPD; and the minimum allowed by some binoculars is still too great for people with a small IPD.
Measuring pupillary distance
Someone with training in the field of optics can accurately measure your pupillary distance. This is normally done with a small millimeter ruler referred to as a "PD stick" or with a corneal reflex pupillometer, which is a machine calibrated to help the optical professional more accurately measure the pupillary distance.In very young children and babies, where the patient is unlikely to stay still, the optical professional will typically measure from one medial canthus
Canthus (anatomy)
Canthus is either corner of the eye where the upper and lower eyelids meet. More specifically, the medial and lateral canthi would be described as the medial and lateral ends/angles of the palpebral fissure....
to the other lateral canthus.
Typical values
- The typical pupillary distance for adults is around 54–68 mm, while measurements generally fall between 48 and 73 mm.
- For children the measurement usually ranges from 41 to 55 mm.
- The 95 percentile adult male in the USA has an IPD of 70 mm (2.8 in) and the 5 percentile, 55 mm (2.17 in). Those are each the 5% of USA men at the far range and short range, respectively.
- For adult females in the USA the figures are 65 and 53 mm (2.6 and 2.1 in).
- For Europeans the figures are 1 mm smaller than the above.
- The IPD is one of the many measurements used in anthropometry, measurements of the human body. The statistical spread of these measurements, usually expressed as percentiles, is used for many purposes. In the case of IPD, it is used in specifying the size range for eyeglasses, binocularsBinocularsBinoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
and other optics such as head-mounted displayHead-mounted displayA head-mounted display or helmet mounted display, both abbreviated HMD, is a display device, worn on the head or as part of a helmet, that has a small display optic in front of one or each eye .- Overview :...
systems. - From the above figures, if a 95 percentile US male and a 5 percentile European female are to be accommodated, the IPD adjustment must be at least 52 – 70 mm, but if adult Japanese people or US/European children are to be included, a lower IPD distance will be required.
In the UK, the PD measurement is classed as a dispensing tool rather than a part of the actual prescription of the person whose eyes were tested, thus there is no obligation for a PD to be provided on patient request.
See also
- PupilometerPupilometerPupilometer is the name used for two different devices—one that measures the distance between pupils, and one that measures the pupil's response to visual stimuli.- Pupillary distance measurement :...
- ODOD- Non abbreviated meanings of OD :* Od , a language of the Oad people* Od, a life force - see Odic force* Od, a Nordic god - see Óðr* Od, a replacement for "God" in some minced oaths- Health and medicine :...
- Oculus sinister