Changes

[[File:Chromostereopsis.png|thumb|200px|Focal conflict due to [[chromostereopsis]]. Look at this image in full screen and feel the eye strain.]]

[[File:VAC detail.png|thumb|200px|VAC as it can happen in virtual reality]]

A '''vergence-accommodation conflict''', also known as a '''focal conflict''', is when a brain receives mismatching cues between eyes' [[focus]] and angle. It is disorienting and can result in eye and brain pain. The effect can be unpleasant and cause eye strain.

A '''vergence-accommodation conflict''' is when a brain receives mismatching cues between eyes' [[focus]] and angle. It is disorienting and can result in eye and brain pain. The effect can be unpleasant and cause eye strain.

Focal conflict can be encountered when viewing flat-focus [[stereogram]]s, [[3D movie]]s, or [[virtual reality]] (VR). It can cause visual fatigue and headaches after a short period of time; It is one of the main contributors to [[virtual reality sickness]]. The phenomenon can make it impossible to focus on objects close to the eye in VR, limiting the development of VR software.<ref name=facebook>{{Citation |title=Vergence-Accommodation Conflict: Facebook Research Explains Why Varifocal Matters For Future VR |url=https://www.youtube.com/watch?v=YWA4gVibKJE |language=en |access-date=2022-09-26| others=This sequence of clips is taken from Douglas Lanman's talk 'Quality Screen Time: Leveraging Computational Displays for Spatial Computing' at the 33d annual Electronic Imaging Symposium (26-30 January 2020)}}</ref>

Focal conflict can be encountered when viewing flat-focus [[stereogram]]s, [[3D movie]]s, or [[virtual reality]] (VR). It can cause visual fatigue and headaches after a short period of time; It is one of the main contributors to [[virtual reality sickness]]. The phenomenon can make it impossible to focus on objects close to the eye in VR, limiting the development of VR software.<ref name=facebook>{{Citation |title=Vergence-Accommodation Conflict: Facebook Research Explains Why Varifocal Matters For Future VR |url=https://www.youtube.com/watch?v=YWA4gVibKJE |language=en |access-date=2022-09-26| others=This sequence of clips is taken from Douglas Lanman's talk 'Quality Screen Time: Leveraging Computational Displays for Spatial Computing' at the 33d annual Electronic Imaging Symposium (26-30 January 2020)}}</ref>

Focal conflict is difficult to overcome when designing new types of [[3D display]]s.<ref name=facebook /> Overcoming focal conflict requires the use of [[integral imaging]], or [[holographic display]]s or [[sequential lightfield display]]s.

Focal conflict is difficult to overcome when designing new types of [[3D display]]s.<ref name=facebook /> Overcoming focal conflict requires the use of [[integral imaging]], or [[holographic display]]s or [[sequential lightfield display]]s.

__NOTOC__

__NOTOC__

== Effects ==

== Effects ==

==Solutions==

==Solutions==

In VR and AR, new types of displays have been developed since the 2010s that can minimize or eliminate focal conflict to non-issue levels. These displays include varifocal, multifocal,<ref>{{Cite journal |last1=Zhan |first1=Tao |last2=Xiong |first2=Jianghao |last3=Zou |first3=Junyu |last4=Wu |first4=Shin-Tson |date=2020-03-30 |title=Multifocal displays: review and prospect |journal=PhotoniX |volume=1 |issue=1 |pages=10 |doi=10.1186/s43074-020-00010-0 |s2cid=214754949 |issn=2662-1991|doi-access=free }}</ref> holographic, [https://www.youtube.com/watch?v=LowxBE6iKQk pin-mirror] and [https://www.youtube.com/watch?v=p5trOS3NaHw light field displays].<ref name=lanman>{{Citation |title=Douglas Lanman (Nvidia) - Light Field Displays at AWE2014 |url=https://www.youtube.com/watch?v=8hLzESOf8SE |language=en |access-date=2022-09-26}}</ref>

In VR and AR, new types of displays have been developed since the 2010s that can minimize or eliminate focal conflict to non-issue levels. These displays include varifocal, multifocal,<ref>{{Cite journal |last1=Zhan |first1=Tao |last2=Xiong |first2=Jianghao |last3=Zou |first3=Junyu |last4=Wu |first4=Shin-Tson |date=2020-03-30 |title=Multifocal displays: review and prospect |journal=PhotoniX |volume=1 |issue=1 |pages=10 |doi=10.1186/s43074-020-00010-0 |s2cid=214754949 |issn=2662-1991|doi-access=free }}</ref> holographic, pin-mirror and light field displays.<ref name=lanman>{{Citation |title=Douglas Lanman (Nvidia) - Light Field Displays at AWE2014 |url=https://www.youtube.com/watch?v=8hLzESOf8SE |language=en |access-date=2022-09-26}}</ref>

Varifocal displays are a concept explored mainly in VR display solutions. The basic principle relies on dynamically adjusting focal distance of displays based on the gaze direction. The technique requires an eye-tracking solution and means of modulating focal distance of a screen. Modulation of a focal distance can be, for example, [https://www.youtube.com/watch?v=JdM5SnSnuyQ&t=4s physical actuation of the screen] in relation to a fixed eyepiece optics, alternatively it can be utilization of varifocal<ref>{{Cite journal |doi=10.1364/OE.27.015627 |title=Design and demonstration of a vari-focal optical see-through head-mounted display using freeform Alvarez lenses |year=2019 |last1=Wilson |first1=Austin |last2=Hua |first2=Hong |journal=Optics Express |volume=27 |issue=11 |pages=15627–15637 |pmid=31163757 |bibcode=2019OExpr..2715627W |s2cid=174815078 |hdl=10150/633572 |hdl-access=free }}</ref><ref>{{Cite book |last1=Stevens |first1=R. E. |last2=Rhodes |first2=D. P. |last3=Hasnain |first3=A. |last4=Laffont |first4=P.-Y. |title=Digital Optics for Immersive Displays |chapter=Varifocal technologies providing prescription and VAC mitigation in HMDS using Alvarez lenses |editor-first1=Bernard C |editor-first2=Hagen |editor-first3=Wolfgang |editor-last1=Kress |editor-last2=Stolle |editor-last3=Osten |date=2018-05-21 |chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10676/106760J/Varifocal-technologies-providing-prescription-and-VAC-mitigation-in-HMDs-using/10.1117/12.2318397.full |publisher=SPIE |volume=10676 |pages=142–158 |doi=10.1117/12.2318397|bibcode=2018SPIE10676E..0JS |isbn=9781510618787 |s2cid=173178593 }}</ref> lens element(s). While varifocal approach mitigates or entirely solves VAC, it cannot convey realistic monocular focus cues. To try to add realism, these techniques rely on [https://www.cl.cam.ac.uk/~rkm38/pdfs/march2022_impact_of_focus_cues.pdf image processing techniques to simulate focus cues].    

Varifocal displays are a concept explored mainly in VR display solutions. The basic principle relies on dynamically adjusting focal distance of displays based on the gaze direction. The technique requires an eye-tracking solution and means of modulating focal distance of a screen. Modulation of a focal distance can be, for example, physical actuation of the screen in relation to a fixed eyepiece optics, alternatively it can be utilization of varifocal<ref>{{Cite journal |doi=10.1364/OE.27.015627 |title=Design and demonstration of a vari-focal optical see-through head-mounted display using freeform Alvarez lenses |year=2019 |last1=Wilson |first1=Austin |last2=Hua |first2=Hong |journal=Optics Express |volume=27 |issue=11 |pages=15627–15637 |pmid=31163757 |bibcode=2019OExpr..2715627W |s2cid=174815078 |hdl=10150/633572 |hdl-access=free }}</ref><ref>{{Cite book |last1=Stevens |first1=R. E. |last2=Rhodes |first2=D. P. |last3=Hasnain |first3=A. |last4=Laffont |first4=P.-Y. |title=Digital Optics for Immersive Displays |chapter=Varifocal technologies providing prescription and VAC mitigation in HMDS using Alvarez lenses |editor-first1=Bernard C |editor-first2=Hagen |editor-first3=Wolfgang |editor-last1=Kress |editor-last2=Stolle |editor-last3=Osten |date=2018-05-21 |chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10676/106760J/Varifocal-technologies-providing-prescription-and-VAC-mitigation-in-HMDs-using/10.1117/12.2318397.full |publisher=SPIE |volume=10676 |pages=142–158 |doi=10.1117/12.2318397|bibcode=2018SPIE10676E..0JS |isbn=9781510618787 |s2cid=173178593 }}</ref> lens element(s). While varifocal approach mitigates or entirely solves VAC, it cannot convey realistic monocular focus cues. To try to add realism, these techniques rely on image processing techniques to simulate focus cues.    

Meta Half Dome prototypes addressed the problem with variable focus lenses that matched focal depth to vergence stereoscopic depth.<ref>{{Cite web |last=VR |first=Oculus |title=Introducing the Team Behind Half Dome—Facebook Reality Labs' Varifocal Prototype {{!}} Meta Quest Blog |url=https://www.oculus.com/blog/introducing-the-team-behind-half-dome-facebook-reality-labs-varifocal-prototype/ |access-date=2023-06-13 |website=www.oculus.com |language=en}}</ref> The first prototype used bulky mechanical actuators to refocus the lens. The third prototype used a stack of 6 liquid crystal lens layers where each layer could be turned on and off by applying a voltage, and this creates 64 discrete focal planes.<ref>{{Cite web |date=2020-07-28 |title=Facebook's Display Research Lead: Varifocal Half-Dome 3 'Almost Ready For Prime Time' |url=https://www.uploadvr.com/half-dome-3-prime-time/ |access-date=2023-06-13 |website=UploadVR |language=en}}</ref> There are currently no production products using this technology.

Meta Half Dome prototypes addressed the problem with variable focus lenses that matched focal depth to vergence stereoscopic depth.<ref>{{Cite web |last=VR |first=Oculus |title=Introducing the Team Behind Half Dome—Facebook Reality Labs' Varifocal Prototype {{!}} Meta Quest Blog |url=https://www.oculus.com/blog/introducing-the-team-behind-half-dome-facebook-reality-labs-varifocal-prototype/ |access-date=2023-06-13 |website=www.oculus.com |language=en}}</ref> The first prototype used bulky mechanical actuators to refocus the lens. The third prototype used a stack of 6 liquid crystal lens layers where each layer could be turned on and off by applying a voltage, and this creates 64 discrete focal planes.<ref>{{Cite web |date=2020-07-28 |title=Facebook's Display Research Lead: Varifocal Half-Dome 3 'Almost Ready For Prime Time' |url=https://www.uploadvr.com/half-dome-3-prime-time/ |access-date=2023-06-13 |website=UploadVR |language=en}}</ref> There are currently no production products using this technology.

Light field displays are one of the best ways to solve the vergence-focal conflict.<ref name="lanman" /> They share features with [[integral imaging]] displays.

Light field displays are one of the best ways to solve the vergence-focal conflict.<ref name="lanman" /> They share features with [[integral imaging]] displays.

[http://www.creal.com CREAL], a near-eye display manufacturer for AR headsets/glasses, developed a light field display technology that projects the light rays just like they exist in the real world. This way, the virtual content has a real depth, and each eye can change focus naturally between the virtual objects, from up close to infinity.

[[CREAL]], a near-eye display manufacturer for AR headsets/glasses, developed a light field display technology that projects the light rays just like they exist in the real world. This way, the virtual content has a real depth, and each eye can change focus naturally between the virtual objects, from up close to infinity.

[[SeeReal Technologies]], a manufacturer of displays for 3D-enabled mobile gadgets, claim that their displays can generate visuals that do not have fixed focus.<ref>{{Cite book|chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/6803/68030M/Large-holographic-displays-as-an-alternative-to-stereoscopic-displays/10.1117/12.766163.full|chapter=Large holographic displays as an alternative to stereoscopic displays|first1=R.|last1=Häussler|first2=A.|last2=Schwerdtner|first3=N.|last3=Leister|editor-first1=Andrew J |editor-first2=Nicolas S |editor-first3=John O |editor-last1=Woods |editor-last2=Holliman |editor-last3=Merritt |title=Stereoscopic Displays and Applications XIX |date=29 February 2008|publisher=SPIE|volume=6803|pages=219–227|via=www.spiedigitallibrary.org|doi=10.1117/12.766163|s2cid=62176480 }}</ref> The company developed the display used in the [[Takee 1]] smartphone.<ref>{{Cite web |last=Kano3D |date=2020-12-29 |title=Takee 1: The first Holographic Smartphone gets a new Update after 6 Years! |url=https://www.tridimensional.info/2020/12/takee-1-the-first-holographic-smartphone-gets-a-new-update-after-6-years/ |access-date=2022-09-28 |website=Tridimensional.info |language=en-US}}</ref> However, SeeReal's solution requires [[eye tracking]], which can limit the 3D capabilities of the displays such as the [[field of view]] of the 3D effect.{{citation needed|date=October 2022}}

[[SeeReal Technologies]], a manufacturer of displays for 3D-enabled mobile gadgets, claim that their displays can generate visuals that do not have fixed focus.<ref>{{Cite book|chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/6803/68030M/Large-holographic-displays-as-an-alternative-to-stereoscopic-displays/10.1117/12.766163.full|chapter=Large holographic displays as an alternative to stereoscopic displays|first1=R.|last1=Häussler|first2=A.|last2=Schwerdtner|first3=N.|last3=Leister|editor-first1=Andrew J |editor-first2=Nicolas S |editor-first3=John O |editor-last1=Woods |editor-last2=Holliman |editor-last3=Merritt |title=Stereoscopic Displays and Applications XIX |date=29 February 2008|publisher=SPIE|volume=6803|pages=219–227|via=www.spiedigitallibrary.org|doi=10.1117/12.766163|s2cid=62176480 }}</ref> The company developed the display used in the [[Takee 1]] smartphone.<ref>{{Cite web |last=Kano3D |date=2020-12-29 |title=Takee 1: The first Holographic Smartphone gets a new Update after 6 Years! |url=https://www.tridimensional.info/2020/12/takee-1-the-first-holographic-smartphone-gets-a-new-update-after-6-years/ |access-date=2022-09-28 |website=Tridimensional.info |language=en-US}}</ref> However, SeeReal's solution requires [[eye tracking]], which can limit the 3D capabilities of the displays such as the [[field of view]] of the multifocality.{{citation needed|date=October 2022}}

==See also==

==See also==

== References ==

== References ==

{{reflist}}

{{reflist}}

[[Category:Visual]]

[[Category:Visual]]

[[Category:Human vision]]

[[Category:Human vision]]