Interpupillary distance
Encyclopedia
Interpupillary distance (IPD) 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, night vision devices or goggles (NVGs), and head-mounted display
s (HMDs). IPD data are used in the design of such systems to specify the range of lateral adjustment of the exit optics or eyepieces. IPD is also used to describe the distance between the exit pupils or optical axes of a binocular optical system.
Pupillary distance
(PD) also describes the distance between the two pupils, but is an optometric term used to specify prescription eyewear. The PD of a patient is used to specify prescriptive eyewear for that patient. The distinction with IPD is the importance of anthropometric databases and the design of binocular viewing devices with an IPD adjustment that will fit a targeted population of users.
. This device presents a simple binocular target that can be set from a close viewing distance out to optical infinity. Closer settings will result in an IPD reduction associated with convergent eyepieces. Some pupilometers provide a separate distance readout for the left- and right-eye—taking ocular asymmetry into account.
s have small exit pupils, and adjustment for user IPD is necessary. 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. A Blue Light Industry stereo microscope is a typical device, and has an ajustment range of 55 to 75 mm. In contrast to microscopes, the weight and bulk of NVGs and HMDs are large factors for wearing comfort and usability. The ANVIS NVG has an adjustment range of 52 to 72 mm. The Rockwell-Collins Optronics XL35 and XL50 binocular HMDs have a range of 55 to 75 mm. The 1988 Army Survey can be used to evaluate the percentage of the Army population captured by these ranges.
Binocular HMDs can be designed with a fixed IPD to minimize weight, bulk and cost. The fixed-IPD design strategy assumes that the exit pupil will be large enough to capture the IPD range of a targeted population. An adjustable IPD design assumes that the lateral adjustment range in conjunction with the exit pupil size is required to capture the targeted population.
. For example, a bench-top haploscope
may require setting the mirror separation for each experimental subject. Other experimental presentations may require the use of IPD to control for ocular convergence and binocular depth.
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. Hyperstereopsis increases ocular convergence and causes near objects to appear closer and with exaggerated depth and slant.
Head-mounted display
A 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 :...
s (HMDs). IPD data are used in the design of such systems to specify the range of lateral adjustment of the exit optics or eyepieces. IPD is also used to describe the distance between the exit pupils or optical axes of a binocular optical system.
Pupillary distance
Pupillary distance
Pupillary Distance or interpupillary distance is the distance between the centers of the pupils in each eye. This measurement is used when preparing to make prescription eyeglasses...
(PD) also describes the distance between the two pupils, but is an optometric term used to specify prescription eyewear. The PD of a patient is used to specify prescriptive eyewear for that patient. The distinction with IPD is the importance of anthropometric databases and the design of binocular viewing devices with an IPD adjustment that will fit a targeted population of users.
Measurement
IPD can be precisely measured with a pupilometerPupilometer
Pupilometer 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 :...
. This device presents a simple binocular target that can be set from a close viewing distance out to optical infinity. Closer settings will result in an IPD reduction associated with convergent eyepieces. Some pupilometers provide a separate distance readout for the left- and right-eye—taking ocular asymmetry into account.
Databases
Anthropometric databases are available that include IPD. These include Military Handbook 743A and the 1988 Anthropometric Survey of US Army Personnel. These databases express the IPD for each gender and sample size (n) as the mean and standard deviation, minimum and maximum, and percentiles (e.g., 5th and 95th; 1st and 99th, 50th or median). Representative data from the 1988 Anthropometric Survey are shown in the following table.| m/f | n | mean | sd | min | max | 1st | 5th | 50th | 95th | 99th |
|---|---|---|---|---|---|---|---|---|---|---|
| m | 1771 | 64.7 | 3.7 | 52 | 78 | 57 | 59 | 65 | 71 | 74 |
| f | 2205 | 62.3 | 3.6 | 52 | 76 | 55 | 57 | 62 | 69 | 71 |
Viewing devices
Devices such as stereo microscopeStereo microscope
The stereo or dissecting microscope is an optical microscope variant designed for low magnification observation or a sample using incident light illumination rather than transillumination. It uses two separate optical paths with two objectives and two eyepieces to provide slightly different viewing...
s have small exit pupils, and adjustment for user IPD is necessary. 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. A Blue Light Industry stereo microscope is a typical device, and has an ajustment range of 55 to 75 mm. In contrast to microscopes, the weight and bulk of NVGs and HMDs are large factors for wearing comfort and usability. The ANVIS NVG has an adjustment range of 52 to 72 mm. The Rockwell-Collins Optronics XL35 and XL50 binocular HMDs have a range of 55 to 75 mm. The 1988 Army Survey can be used to evaluate the percentage of the Army population captured by these ranges.
Binocular HMDs can be designed with a fixed IPD to minimize weight, bulk and cost. The fixed-IPD design strategy assumes that the exit pupil will be large enough to capture the IPD range of a targeted population. An adjustable IPD design assumes that the lateral adjustment range in conjunction with the exit pupil size is required to capture the targeted population.
Other applications
IPD is also used in binocular vision scienceVision science
Vision science is the science dedicated to the interdisciplinary study of visual perception and the visual system. Vision scientists study various aspects of vision from the perspectives of cognitive psychology, neuroscience, computer science, psychophysics, and ophthalmology.- See also :* Visual...
. For example, a bench-top haploscope
Haploscope
A haploscope is an optical device for presenting one image to one eye and another image to the other eye. The word derives from two Greek roots: haploieides, single and skopeo, to view. The word is often used interchangeably with stereoscope, but it is more general than that. A stereoscope is a...
may require setting the mirror separation for each experimental subject. Other experimental presentations may require the use of IPD to control for ocular convergence and binocular depth.
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. Hyperstereopsis increases ocular convergence and causes near objects to appear closer and with exaggerated depth and slant.