Interpupillary distance - Revision history

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	[[Category:Terms]]		[[Category:Terms]]
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	[[Category:Human visual system]]		[[Category:Human visual system]]
	[[Category:Virtual reality hardware]]		[[Category:Virtual reality hardware]]

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	[[Category:Terms]]		[[Category:Terms]]
	[[Category:Human ~~vision~~]]		[[Category:Human visual system]]

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	Developers can change the sense of scale by changing virtual IPD. They can cause the environment to increase or decrease in size by changing the virtual IPD.		Developers can change the sense of scale by changing virtual IPD. They can cause the environment to increase or decrease in size by changing the virtual IPD.

			==References==
			{{Reflist}}

	[[Category:Terms]]		[[Category:Terms]]
	[[Category:Human vision]]		[[Category:Human vision]]

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	[[File:Average IPD.png\|thumb\|250px\|A bar chart of average IPD in humans]]		[[File:Average IPD.png\|thumb\|250px\|A bar chart of average IPD in humans]]
	'''Interpupillary distance''' ('''IPD''') is the distance between the pupils of your eyes. There are two types of IPDs: ~~[[#~~Real IPD~~\|Real IPD]]~~ and ~~[[#Virtual IPD\|~~Virtual IPD]].		'''Interpupillary distance''' ('''IPD''') is the distance between the pupils of your eyes. There are two types of IPDs: Real IPD and Virtual IPD.

	Most adult humans have an IPD of about 63mm.		Most adult humans have an IPD of about 63mm.

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 [[File:Average IPD.png|thumb|250px|A bar chart of average IPD in humans]]
 '''Interpupillary distance''' ('''IPD''') is the distance between the pupils of your eyes. There are two types of IPDs: [[#Real IPD|Real IPD]] and [[#Virtual IPD|Virtual IPD]].
 ==Real IPD==
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			[[File:Average IPD.png\|thumb\|250px\|A bar chart of average IPD in humans]]
	'''Interpupillary distance''' ('''IPD''') is the distance between the pupils of your eyes. There are two types of IPDs: [[#Real IPD\|Real IPD]] and [[#Virtual IPD\|Virtual IPD]].		'''Interpupillary distance''' ('''IPD''') is the distance between the pupils of your eyes. There are two types of IPDs: [[#Real IPD\|Real IPD]] and [[#Virtual IPD\|Virtual IPD]].

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	The brain's visual cortex processes and fuses these two 2D images into a single, unified perception with an added dimension of depth. This process, known as '''[[stereopsis]]''', is the basis for high-fidelity depth perception, allowing for precise judgments of distance and the three-dimensional structure of objects.<ref name="StereoscopicVR" /> The magnitude of the IPD directly influences the amount of binocular disparity; a wider IPD results in a greater difference between the two eyes' views, which can enhance the stereoscopic effect.		The brain's visual cortex processes and fuses these two 2D images into a single, unified perception with an added dimension of depth. This process, known as '''[[stereopsis]]''', is the basis for high-fidelity depth perception, allowing for precise judgments of distance and the three-dimensional structure of objects.<ref name="StereoscopicVR" /> The magnitude of the IPD directly influences the amount of binocular disparity; a wider IPD results in a greater difference between the two eyes' views, which can enhance the stereoscopic effect.

	'''Horizontal disparity''', defined as the difference between viewing angles from each eye to an object, drives stereoscopic depth sensation. The '''horopter''' depicts points with zero disparity relative to ~~fixation—points~~ at the same depth as the fixation point project onto corresponding locations in both retinas. Objects closer than the horopter have '''crossed disparity''' (negative), while objects farther have '''parallel disparity''' (positive). Within '''Panum's fusional area'''~~—the~~ region of binocular single ~~vision—points~~ off the horopter have disparity but are still seen as single and in depth relative to fixation. Outside this area, physiological [[diplopia]] (double vision) occurs.		'''Horizontal disparity''', defined as the difference between viewing angles from each eye to an object, drives stereoscopic depth sensation. The '''horopter''' depicts points with zero disparity relative to fixation, points at the same depth as the fixation point project onto corresponding locations in both retinas. Objects closer than the horopter have '''crossed disparity''' (negative), while objects farther have '''parallel disparity''' (positive). Within '''Panum's fusional area''', the region of binocular single vision, points off the horopter have disparity but are still seen as single and in depth relative to fixation. Outside this area, physiological [[diplopia]] (double vision) occurs.

	==Real IPD==		==Real IPD==
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	===Aligning the User with the Virtual World===		===Aligning the User with the Virtual World===

	A VR/AR headset works by presenting a separate, slightly different image to each eye, simulating binocular disparity to create the illusion of depth. To achieve this effectively, the optical ~~system—composed~~ of displays and ~~lenses—must~~ be precisely aligned with the user's visual system. The primary goal of IPD adjustment is to horizontally position the optical center of each lens directly in front of the center of each pupil.<ref name="MetaIPD" />		A VR/AR headset works by presenting a separate, slightly different image to each eye, simulating binocular disparity to create the illusion of depth. To achieve this effectively, the optical system, composed of displays and lenses, must be precisely aligned with the user's visual system. The primary goal of IPD adjustment is to horizontally position the optical center of each lens directly in front of the center of each pupil.<ref name="MetaIPD" />

	This alignment ensures that the user is looking through the lens's '''optical sweet spot''', also known as the '''[[eyebox]]'''. The eyebox is the three-dimensional volume where the eye can be positioned to receive a clear, full, and undistorted view of the virtual image.<ref name="RoadToVR-Measure" /><ref name="EyeboxVR" /> VR lenses have a central area of maximum clarity called the "sweet spot" or "optical center," typically 15–25 mm in diameter for [[Fresnel lens]]es and larger for [[pancake lens]]es.		This alignment ensures that the user is looking through the lens's '''optical sweet spot''', also known as the '''[[eyebox]]'''. The eyebox is the three-dimensional volume where the eye can be positioned to receive a clear, full, and undistorted view of the virtual image.<ref name="RoadToVR-Measure" /><ref name="EyeboxVR" /> VR lenses have a central area of maximum clarity called the "sweet spot" or "optical center," typically 15–25 mm in diameter for [[Fresnel lens]]es and larger for [[pancake lens]]es.
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	===Hardware IPD (Lens Spacing)===		===Hardware IPD (Lens Spacing)===

	'''Hardware IPD''' refers to the physical distance between the optical centers of the two lenses inside the HMD.<ref name="MetaIPD" /> The adjustment mechanism on a ~~headset—whether~~ it's a slider, knob, or automated ~~motor—directly~~ changes this lens spacing. The goal of adjusting the hardware IPD is to physically align the lenses with the user's pupils, placing them in the center of the eyebox to achieve maximum image clarity and minimize optical aberrations.<ref name="MilvusIPD" />		'''Hardware IPD''' refers to the physical distance between the optical centers of the two lenses inside the HMD.<ref name="MetaIPD" /> The adjustment mechanism on a headset, whether it's a slider, knob, or automated motor, directly changes this lens spacing. The goal of adjusting the hardware IPD is to physically align the lenses with the user's pupils, placing them in the center of the eyebox to achieve maximum image clarity and minimize optical aberrations.<ref name="MilvusIPD" />

	Hardware adjustment provides optical alignment where eyes look through the optical center, achieving maximum clarity, full resolution and sharpness, designed field of view specifications, reduced eye strain, and physical comfort.		Hardware adjustment provides optical alignment where eyes look through the optical center, achieving maximum clarity, full resolution and sharpness, designed field of view specifications, reduced eye strain, and physical comfort.
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	The '''eyebox''' is the three-dimensional volume within which a user's eye pupil must be located to see the entire, un-vignetted, and clear image produced by the HMD's lens.<ref name="OpticaEyebox" /> The center of this volume, where image quality is highest, is often called the '''optical sweet spot'''.<ref name="RoadToVR-Measure" />		The '''eyebox''' is the three-dimensional volume within which a user's eye pupil must be located to see the entire, un-vignetted, and clear image produced by the HMD's lens.<ref name="OpticaEyebox" /> The center of this volume, where image quality is highest, is often called the '''optical sweet spot'''.<ref name="RoadToVR-Measure" />

	Moving the eye outside the ~~eyebox—either~~ horizontally, vertically, or in depth ([[eye relief]])~~—will~~ result in a degraded image, with effects like blurring, [[chromatic aberration]], or vignetting (the edges of the image being cut off). The purpose of hardware IPD adjustment is to horizontally position the user's pupils within the eyeboxes of the two lenses. A headset with a larger eyebox is more forgiving of small IPD misalignments and headset movement on the user's face, contributing to a more comfortable and consistent experience.<ref name="AvantierVR" />		Moving the eye outside the eyebox, either horizontally, vertically, or in depth ([[eye relief]]), will result in a degraded image, with effects like blurring, [[chromatic aberration]], or vignetting (the edges of the image being cut off). The purpose of hardware IPD adjustment is to horizontally position the user's pupils within the eyeboxes of the two lenses. A headset with a larger eyebox is more forgiving of small IPD misalignments and headset movement on the user's face, contributing to a more comfortable and consistent experience.<ref name="AvantierVR" />

	==Lens Design Impact on IPD Requirements==		==Lens Design Impact on IPD Requirements==
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	===Breakthrough Year: 2016===		===Breakthrough Year: 2016===

	'''March ~~2016—Oculus~~ Rift CV1''' launched with mechanical adjustment via physical slider offering smooth continuous adjustment across approximately 58–72 mm range, making it the first mainstream consumer headset with hardware IPD adjustment. Over 500,000 units sold in the first year.		'''March 2016-Oculus Rift CV1''' launched with mechanical adjustment via physical slider offering smooth continuous adjustment across approximately 58–72 mm range, making it the first mainstream consumer headset with hardware IPD adjustment. Over 500,000 units sold in the first year.

	'''April ~~2016—HTC~~ Vive''' launched with mechanical adjustment knob providing rotary continuous adjustment across approximately 60–75 mm range, setting the standard for enthusiast VR with room-scale tracking.		'''April 2016-HTC Vive''' launched with mechanical adjustment knob providing rotary continuous adjustment across approximately 60–75 mm range, setting the standard for enthusiast VR with room-scale tracking.

	'''October ~~2016—PlayStation~~ VR''' launched with mechanical adjustment via slider (~58–70 mm), selling millions of units to achieve the largest installed base at the time.		'''October 2016-PlayStation VR''' launched with mechanical adjustment via slider (~58–70 mm), selling millions of units to achieve the largest installed base at the time.

	The significance of 2016 established the industry standard where mechanical IPD adjustment became expected, making VR a viable consumer product category.		The significance of 2016 established the industry standard where mechanical IPD adjustment became expected, making VR a viable consumer product category.
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	===The Regression: Cost-Cutting Era (2019–2020)===		===The Regression: Cost-Cutting Era (2019–2020)===

	'''March ~~2019—Oculus~~ Rift S''' represented a significant backward step, launching with fixed IPD at 63.5 ~~mm—identical~~ to DK2 from ~~2014—with~~ software-only adjustment. The "best fit" range spanned only 61.5–65.5 mm (4 mm total). ANSUR II analysis showed only 46% of men and 43% of women fit "best" compared to 99%/93% with mechanical adjustment. Massive community backlash ensued, with many refusing to buy.<ref name="PalmerLuckey" />		'''March 2019-Oculus Rift S''' represented a significant backward step, launching with fixed IPD at 63.5 mm, identical to DK2 from 2014, with software-only adjustment. The "best fit" range spanned only 61.5–65.5 mm (4 mm total). ANSUR II analysis showed only 46% of men and 43% of women fit "best" compared to 99%/93% with mechanical adjustment. Massive community backlash ensued, with many refusing to buy.<ref name="PalmerLuckey" />

	'''September ~~2020—Oculus~~ Quest 2''' at $299 offered a three-position compromise with discrete positions at 58 mm, 63 mm, and 68 mm. While better than Rift S, it was worse than Quest 1, yet became the best-selling VR headset ever due to aggressive pricing.		'''September 2020-Oculus Quest 2''' at $299 offered a three-position compromise with discrete positions at 58 mm, 63 mm, and 68 mm. While better than Rift S, it was worse than Quest 1, yet became the best-selling VR headset ever due to aggressive pricing.

	===Innovation and Automation Era (2021–Present)===		===Innovation and Automation Era (2021–Present)===
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	* '''Take breaks immediately''' if discomfort occurs		* '''Take breaks immediately''' if discomfort occurs

	Medical consensus indicates that short-term ~~effects—eye~~ fatigue, blurred vision, ~~headaches—are~~ common but resolve within minutes to hours. No proven permanent damage occurs in healthy adults with proper use, though children under 6 should avoid displays causing vergence-accommodation conflict. Red flags requiring medical attention include symptoms lasting more than 24 hours, progressive worsening, or persistent double vision.		Medical consensus indicates that short-term effects, eye fatigue, blurred vision, headaches, are common but resolve within minutes to hours. No proven permanent damage occurs in healthy adults with proper use, though children under 6 should avoid displays causing vergence-accommodation conflict. Red flags requiring medical attention include symptoms lasting more than 24 hours, progressive worsening, or persistent double vision.

	==See Also==		==See Also==

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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 (~~e.g.,~~ 2 meters).<ref name="MetaIPD" /><ref name="FittingBox" />		* '''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 (~~e.g.,~~ 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.		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 (~~e.g.,~~ 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 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 (~~e.g.,~~ 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.		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 (~~e.g.,~~ 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 (~~e.g.,~~ an object 30 cm away), your eyes must ''verge'' to that closer 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.