Interpupillary distance: Difference between revisions
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The distance between the pupils changes depending on whether the eyes are focused on a distant or a near object, due to the mechanism of [[convergence (eye)|eye convergence]].<ref name="DistanceNearPD" /> | The distance between the pupils changes depending on whether the eyes are focused on a distant or a near object, due to the mechanism of [[convergence (eye)|eye convergence]].<ref name="DistanceNearPD" /> | ||
* '''Distance PD''' (also called '''Far PD''') is the measurement taken when the eyes are looking at a distant object, causing the lines of sight to be effectively parallel. This is the standard measurement required for single-vision distance glasses, the upper portion of [[bifocal]]s, and most importantly, for setting up VR and AR headsets, which typically have a fixed optical focus set at a distance ( | * '''Distance PD''' (also called '''Far PD''') is the measurement taken when the eyes are looking at a distant object, causing the lines of sight to be effectively parallel. This is the standard measurement required for single-vision distance glasses, the upper portion of [[bifocal]]s, and most importantly, for setting up VR and AR headsets, which typically have a fixed optical focus set at a distance (for example 2 meters).<ref name="MetaIPD" /><ref name="FittingBox" /> | ||
* '''Near PD''' is the measurement taken when the eyes converge to focus on a close object, such as a book or a smartphone (typically at a distance of about 40 cm). Because the eyes turn inward, the Near PD is always smaller than the Distance PD, typically by 3 to 4 millimeters.<ref name="WebMD" /><ref name="DistanceNearPD" /> This measurement is essential for fitting reading glasses or the near-vision segments of bifocal and [[progressive lens]]es. | * '''Near PD''' is the measurement taken when the eyes converge to focus on a close object, such as a book or a smartphone (typically at a distance of about 40 cm). Because the eyes turn inward, the Near PD is always smaller than the Distance PD, typically by 3 to 4 millimeters.<ref name="WebMD" /><ref name="DistanceNearPD" /> This measurement is essential for fitting reading glasses or the near-vision segments of bifocal and [[progressive lens]]es. | ||
A common source of error for VR users is inadvertently measuring their Near PD when they require their Distance PD. Many self-measurement guides instruct the user to stand close to a mirror ( | A common source of error for VR users is inadvertently measuring their Near PD when they require their Distance PD. Many self-measurement guides instruct the user to stand close to a mirror (for example 8 inches away). If the user focuses on their own reflection at this close range, their eyes will converge, yielding an inaccurate Near PD measurement. To correctly measure Distance PD using a mirror, the user must focus on a distant object reflected in the mirror, ensuring their eyes remain parallel. | ||
===Binocular PD vs. Monocular PD=== | ===Binocular PD vs. Monocular PD=== | ||
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===Average Values and Population Range=== | ===Average Values and Population Range=== | ||
The average adult real IPD is around 63–64 mm, with males tending to have slightly larger IPDs on average than females ( | The average adult real IPD is around 63–64 mm, with males tending to have slightly larger IPDs on average than females (for example about 64.0 mm in adult males vs 61.7 mm in adult females in large surveys).<ref name="Dodgson2004" /><ref name="ANSUR" /> Most adults fall within roughly 50 mm to 75 mm, and only a small percentage have IPDs outside that range.<ref name="Dodgson2004" /><ref name="ClevelandClinic" /> In extreme cases, adult IPDs as low as ~45 mm or as high as ~80 mm have been recorded.<ref name="Dodgson2004" /> | ||
The most comprehensive dataset comes from the 2012 ANSUR II U.S. Army Anthropometric Survey of 6,068 soldiers: | The most comprehensive dataset comes from the 2012 ANSUR II U.S. Army Anthropometric Survey of 6,068 soldiers: | ||
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* '''Incorrect Sense of Scale''': A direct consequence of distorted depth perception is an incorrect [[sense of scale]]. If the rendered IPD is wider than the user's IPD, the world can feel miniaturized, like a "dollhouse". Conversely, if the rendered IPD is narrower, the world can feel gigantic.<ref name="RedditPSVRScale" /><ref name="KholdScale" /> | * '''Incorrect Sense of Scale''': A direct consequence of distorted depth perception is an incorrect [[sense of scale]]. If the rendered IPD is wider than the user's IPD, the world can feel miniaturized, like a "dollhouse". Conversely, if the rendered IPD is narrower, the world can feel gigantic.<ref name="RedditPSVRScale" /><ref name="KholdScale" /> | ||
Research indicates that even small mismatches ( | Research indicates that even small mismatches (for example 5 mm) can reduce visual acuity and comfort, particularly in high-resolution HMDs.<ref name="IEEEVR" /> For AR, IPD affects overlay alignment with the real world, impacting tasks like surgical simulation or navigation. | ||
==IPD in Various VR/AR Headsets== | ==IPD in Various VR/AR Headsets== | ||
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* '''Accommodation''' is the focusing of the crystalline lens in the eye to bring that object's image into sharp focus on the retina. | * '''Accommodation''' is the focusing of the crystalline lens in the eye to bring that object's image into sharp focus on the retina. | ||
In the real world, these two actions are tightly coupled by a neurological reflex; when you look at a near object, your eyes both converge and refocus simultaneously. In most VR headsets, however, the displays are at a fixed physical distance, and the lenses place the virtual image at a fixed optical distance ( | In the real world, these two actions are tightly coupled by a neurological reflex; when you look at a near object, your eyes both converge and refocus simultaneously. In most VR headsets, however, the displays are at a fixed physical distance, and the lenses place the virtual image at a fixed optical distance (for example 2 meters). This means your eyes must ''accommodate'' to this fixed distance at all times. Yet, to view virtual objects that are rendered at different depths (for example an object 30 cm away), your eyes must ''verge'' to that closer distance. | ||
This decoupling of vergence and accommodation creates a sensory conflict that can lead to eye strain, fatigue, and nausea.<ref name="VACTaylor" /> While an incorrect IPD setting does not cause VAC, it adds another layer of strain to the visual system, exacerbating the discomfort caused by the conflict. IPD mismatch creates a "double burden" effect, forcing optical compensation while simultaneously struggling with VAC from fixed-focus displays. | This decoupling of vergence and accommodation creates a sensory conflict that can lead to eye strain, fatigue, and nausea.<ref name="VACTaylor" /> While an incorrect IPD setting does not cause VAC, it adds another layer of strain to the visual system, exacerbating the discomfort caused by the conflict. IPD mismatch creates a "double burden" effect, forcing optical compensation while simultaneously struggling with VAC from fixed-focus displays. | ||