Changes

[[File:VAC segment.png|thumb|right|300px|Focal conflict in VR]]

[[File:VAC segment.png|thumb|right|300px|Focus conflict in VR]]

A '''focus conflict''' is when a brain receives mismatching cues between eyes' [[focus]] and [[vergence]]. The effect can be unpleasant and cause eye strain. This can happen with fixed-focus biscopic displays, such as the [[Meta Quest]], [[Oculus Rift]], and [[HoloLens]].

A '''focus conflict''' is when a brain receives mismatching cues between eyes' [[focus]] and [[vergence]]. The effect can be unpleasant and cause eye strain. This can happen with fixed-focus biscopic displays, such as the [[Meta Quest]], [[Oculus Rift]], and [[HoloLens]].

Focal conflict can occur in [[virtual reality]] devices, [[augmented reality]] devices, and binocular flat focus autostereoscopic displays.  

Focus conflict can occur in [[virtual reality]] devices, [[augmented reality]] devices, and binocular flat focus autostereoscopic displays.  

When a human views the real world, vergence and focus distances typically match, and the human visual system has evolved to expect this.

When a human views the real world, vergence and focus distances typically match, and the human visual system has evolved to expect this.

Fixed-focus biscopic displays have a fixed focus distance, but the vergence distance can change widely, resulting in a mismatch. The human visual system has not evolved to view these types of artificial 3D images comfortably. Focal conflict can be a very unpleasant sensation for the viewer.<ref>{{Cite journal |title=The zone of comfort: Predicting visual discomfort with stereo displays |url=https://jov.arvojournals.org/article.aspx?articleid=2121032 |journal=Jov ArvoJournals |volume=11 |issue=8}}</ref><ref>{{Cite journal |last1=Wann |first1=John P. |last2=Mon-Williams |first2=Mark |date=May 1997 |title=Health issues with virtual reality displays: what we do know and what we don't |url=https://dl.acm.org/doi/10.1145/271283.271307 |journal=ACM SIGGRAPH Computer Graphics |language=en |volume=31 |issue=2 |pages=53–57 |doi=10.1145/271283.271307 |s2cid=17366319 |issn=0097-8930}}</ref><ref>{{Cite journal |date=March 2008 |title=Vergence–accommodation conflicts hinder visual performance and cause visual fatigue |url=https://jov.arvojournals.org/article.aspx?articleid=2122611 |journal=JOV Arvo Journals |volume=8 |issue=3}}</ref>

Fixed-focus biscopic displays have a fixed focus distance, but the vergence distance can change widely, resulting in a mismatch. The human visual system has not evolved to view these types of artificial 3D images comfortably. Focus conflict can be a very unpleasant sensation for the viewer.<ref>{{Cite journal |title=The zone of comfort: Predicting visual discomfort with stereo displays |url=https://jov.arvojournals.org/article.aspx?articleid=2121032 |journal=Jov ArvoJournals |volume=11 |issue=8}}</ref><ref>{{Cite journal |last1=Wann |first1=John P. |last2=Mon-Williams |first2=Mark |date=May 1997 |title=Health issues with virtual reality displays: what we do know and what we don't |url=https://dl.acm.org/doi/10.1145/271283.271307 |journal=ACM SIGGRAPH Computer Graphics |language=en |volume=31 |issue=2 |pages=53–57 |doi=10.1145/271283.271307 |s2cid=17366319 |issn=0097-8930}}</ref><ref>{{Cite journal |date=March 2008 |title=Vergence–accommodation conflicts hinder visual performance and cause visual fatigue |url=https://jov.arvojournals.org/article.aspx?articleid=2122611 |journal=JOV Arvo Journals |volume=8 |issue=3}}</ref>

Focal conflict is often encountered when viewing [[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>

Focus conflict is often encountered when viewing [[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 very difficult to overcome when designing new types of [[3D display]]s.<ref name=facebook />

Focus conflict is very difficult to overcome when designing new types of [[3D display]]s.<ref name=facebook />

== Effects ==

== Effects ==

Focal conflict is part of why VR and 3D media causes eye strain and is disorienting.<ref>{{Cite web |title=Is it normal the 3DS effect hurt my eyes? - Nintendo 3DS |url=https://gamefaqs.gamespot.com/boards/997614-nintendo-3ds/72524629 |access-date=2022-09-26 |website=gamefaqs.gamespot.com}}</ref> There is not a strong consensus on the extent of visual damage, if any, that may occur due to overexposure to vergence-focus conflict. Even though this is the case, users of classic stereoscopic devices report being unable to look at the 3D screen for a long period of time.<ref>{{Cite web |title=Is Your Nintendo 3DS Bad for Your Health? |url=https://www.pcmag.com/archive/is-your-nintendo-3ds-bad-for-your-health-262584 |access-date=2022-09-26 |website=PCMAG |language=en}}</ref>

Focus conflict is part of why VR and 3D media causes eye strain and is disorienting.<ref>{{Cite web |title=Is it normal the 3DS effect hurt my eyes? - Nintendo 3DS |url=https://gamefaqs.gamespot.com/boards/997614-nintendo-3ds/72524629 |access-date=2022-09-26 |website=gamefaqs.gamespot.com}}</ref> There is not a strong consensus on the extent of visual damage, if any, that may occur due to overexposure to vergence-focus conflict. Even though this is the case, users of classic stereoscopic devices report being unable to look at the 3D screen for a long period of time.<ref>{{Cite web |title=Is Your Nintendo 3DS Bad for Your Health? |url=https://www.pcmag.com/archive/is-your-nintendo-3ds-bad-for-your-health-262584 |access-date=2022-09-26 |website=PCMAG |language=en}}</ref>

== Measurement ==

== Measurement ==

Focal conflict can be quantified; typically, by comparing the [[optical power]] required to focus on objects at the vergence distance with the optical power required to focus on objects at the focus distance.<ref name="Shibata 11–11">{{Cite journal |last1=Shibata |first1=Takashi |last2=Kim |first2=Joohwan |last3=Hoffman |first3=David M. |last4=Banks |first4=Martin S. |date=2011-07-05 |title=The zone of comfort: Predicting visual discomfort with stereo displays |url=https://jov.arvojournals.org/article.aspx?articleid=2121032 |journal=Journal of Vision |language=en |volume=11 |issue=8 |pages=11 |doi=10.1167/11.8.11 |pmid=21778252 |pmc=3369815 |issn=1534-7362}}</ref> In this context, optical power is equal to the reciprocal of distance, with units of [[Dioptre|Diopter]] (m⁻¹). Hence the difference between the reciprocal of the vergence distance and the reciprocal of the focus distance characterizes the extent of vergence-focus conflict.

Focus conflict can be quantified; typically, by comparing the [[optical power]] required to focus on objects at the vergence distance with the optical power required to focus on objects at the focus distance.<ref name="Shibata 11–11">{{Cite journal |last1=Shibata |first1=Takashi |last2=Kim |first2=Joohwan |last3=Hoffman |first3=David M. |last4=Banks |first4=Martin S. |date=2011-07-05 |title=The zone of comfort: Predicting visual discomfort with stereo displays |url=https://jov.arvojournals.org/article.aspx?articleid=2121032 |journal=Journal of Vision |language=en |volume=11 |issue=8 |pages=11 |doi=10.1167/11.8.11 |pmid=21778252 |pmc=3369815 |issn=1534-7362}}</ref> In this context, optical power is equal to the reciprocal of distance, with units of [[Dioptre|Diopter]] (m⁻¹). Hence the difference between the reciprocal of the vergence distance and the reciprocal of the focus distance characterizes the extent of vergence-focus conflict.

In the example of a virtual reality head-mounted display, the focus distance corresponds to the distance of the virtual image plane. Often the optics is designed to place a virtual screen somewhere between 2 meters and infinity. That is, for a virtual display at a 2-meter distance, the target focus distance expressed in diopters is 0.5 D. In contrast, the vergence distance in a stereoscopic display can change freely based on the location of target content. For example, a virtual object by means of binocular disparity can be placed at a 30&nbsp;cm distance, corresponding to 3.33 Diopters. In such a case, the magnitude of the vergence-focus conflict for a person with normal vision would be 3.33-0.5=2.83 diopters.

In the example of a virtual reality head-mounted display, the focus distance corresponds to the distance of the virtual image plane. Often the optics is designed to place a virtual screen somewhere between 2 meters and infinity. That is, for a virtual display at a 2-meter distance, the target focus distance expressed in diopters is 0.5 D. In contrast, the vergence distance in a stereoscopic display can change freely based on the location of target content. For example, a virtual object by means of binocular disparity can be placed at a 30&nbsp;cm distance, corresponding to 3.33 Diopters. In such a case, the magnitude of the vergence-focus conflict for a person with normal vision would be 3.33-0.5=2.83 diopters.

== Physiology ==

== Physiology ==

A vergence-focus conflict is caused due to factors in human physiology like the [[accommodation reflex]]. Focal conflict occurs when the human brain receives mismatching cues between [[vergence]] and [[Accommodation (eye)|accommodation]].<ref name="kramida">{{Cite web |date=2022-09-22 |title=Resolving the Vergence-Accommodation Conflict in Head-Mounted Displays |url=https://3dvar.com/Kramida2016Resolving.pdf |access-date=2022-09-22 |archive-url=https://web.archive.org/web/20220922032435/https://3dvar.com/Kramida2016Resolving.pdf |archive-date=2022-09-22 |url-status=live}}</ref><ref>{{Cite journal |last1=Zhou |first1=Yao |last2=Zhang |first2=Jufan |last3=Fang |first3=Fengzhou |date=2021-12-01 |title=Vergence-accommodation conflict in optical see-through display: review and prospect |journal=Results in Optics |language=en |volume=5 |pages=100160 |doi=10.1016/j.rio.2021.100160 |s2cid=241361232 |issn=2666-9501|doi-access=free }}</ref><ref>{{Cite journal |last=Konrad |first=Robert |date=2015-11-06 |title=What is the vergence-accommodation conflict and how do we fix it? |url=https://doi.org/10.1145/2810048 |journal=XRDS: Crossroads, the ACM Magazine for Students |volume=22 |issue=1 |pages=52–55 |doi=10.1145/2810048 |s2cid=9330080 |issn=1528-4972}}</ref><ref name=anses>{{Cite web |date=2014-11-06 |title=3D technologies and eyesight: use not recommended for children under the age of six, use in moderation for those under the age of 13 |url=https://www.anses.fr/en/content/3d-technologies-and-eyesight-use-not-recommended-children-under-age-six-use-moderation-0 |access-date=2022-09-22 |website=Anses |language=en}}</ref> It often causes headaches and visual fatigue.<ref>{{Cite journal |last1=Hoffman |first1=David M. |last2=Girshick |first2=Ahna R. |last3=Akeley |first3=Kurt |last4=Banks |first4=Martin S. |date=2008-03-01 |title=Vergence–accommodation conflicts hinder visual performance and cause visual fatigue |url=https://jov.arvojournals.org/article.aspx?articleid=2122611 |journal=Journal of Vision |language=en |volume=8 |issue=3 |pages=33.1–30 |doi=10.1167/8.3.33 |issn=1534-7362 |pmc=2879326 |pmid=18484839}}</ref> The vergence-accommodation conflict is one of the main causes of [[virtual reality sickness]].<ref>{{Cite journal |last1=Lawson |first1=Ben D. |last2=Stanney |first2=Kay M. |date=2021 |title=Editorial: Cybersickness in Virtual Reality and Augmented Reality |journal=Frontiers in Virtual Reality |volume=2 |doi=10.3389/frvir.2021.759682 |issn=2673-4192|doi-access=free }}</ref>

A vergence-focus conflict is caused due to factors in human physiology like the [[accommodation reflex]]. Focus conflict occurs when the human brain receives mismatching cues between [[vergence]] and [[Accommodation (eye)|accommodation]].<ref name="kramida">{{Cite web |date=2022-09-22 |title=Resolving the Vergence-Accommodation Conflict in Head-Mounted Displays |url=https://3dvar.com/Kramida2016Resolving.pdf |access-date=2022-09-22 |archive-url=https://web.archive.org/web/20220922032435/https://3dvar.com/Kramida2016Resolving.pdf |archive-date=2022-09-22 |url-status=live}}</ref><ref>{{Cite journal |last1=Zhou |first1=Yao |last2=Zhang |first2=Jufan |last3=Fang |first3=Fengzhou |date=2021-12-01 |title=Vergence-accommodation conflict in optical see-through display: review and prospect |journal=Results in Optics |language=en |volume=5 |pages=100160 |doi=10.1016/j.rio.2021.100160 |s2cid=241361232 |issn=2666-9501|doi-access=free }}</ref><ref>{{Cite journal |last=Konrad |first=Robert |date=2015-11-06 |title=What is the vergence-accommodation conflict and how do we fix it? |url=https://doi.org/10.1145/2810048 |journal=XRDS: Crossroads, the ACM Magazine for Students |volume=22 |issue=1 |pages=52–55 |doi=10.1145/2810048 |s2cid=9330080 |issn=1528-4972}}</ref><ref name=anses>{{Cite web |date=2014-11-06 |title=3D technologies and eyesight: use not recommended for children under the age of six, use in moderation for those under the age of 13 |url=https://www.anses.fr/en/content/3d-technologies-and-eyesight-use-not-recommended-children-under-age-six-use-moderation-0 |access-date=2022-09-22 |website=Anses |language=en}}</ref> It often causes headaches and visual fatigue.<ref>{{Cite journal |last1=Hoffman |first1=David M. |last2=Girshick |first2=Ahna R. |last3=Akeley |first3=Kurt |last4=Banks |first4=Martin S. |date=2008-03-01 |title=Vergence–accommodation conflicts hinder visual performance and cause visual fatigue |url=https://jov.arvojournals.org/article.aspx?articleid=2122611 |journal=Journal of Vision |language=en |volume=8 |issue=3 |pages=33.1–30 |doi=10.1167/8.3.33 |issn=1534-7362 |pmc=2879326 |pmid=18484839}}</ref> The vergence-accommodation conflict is one of the main causes of [[virtual reality sickness]].<ref>{{Cite journal |last1=Lawson |first1=Ben D. |last2=Stanney |first2=Kay M. |date=2021 |title=Editorial: Cybersickness in Virtual Reality and Augmented Reality |journal=Frontiers in Virtual Reality |volume=2 |doi=10.3389/frvir.2021.759682 |issn=2673-4192|doi-access=free }}</ref>

Two ocular responses exist: vergence of eyes, and focus, also known as accommodation. Both of these mechanisms are crucial in stereoscopic vision. Vergence or independent inward/outward rotation of eyes is engaged to fixate on objects and perceive them as single. Incorrect vergence response can cause double vision. Accommodation is the eye’s focusing mechanism and it is engaged to produce a sharp image on a retina. Both of these mechanisms are neurally linked forming the accommodation-convergence reflex<ref>{{Cite web |title=Reflex action {{!}} Definition, Types and Mechanism and Important solved questions |date=11 November 2020 |url=https://www.crackyourtarget.com/reflex-action.html}}</ref> of eyes. One can distinguish vergence {{nowrap|distance{{px2}}{{mdash}}{{px2}}}}a distance of a point towards which both eyes are converging, and an accommodation {{nowrap|distance{{px2}}{{mdash}}{{px2}}}}a distance of a region in space towards which the focus or refractive power of the crystalline lens has been adjusted to produce a sharp image on the retina.

Two ocular responses exist: vergence of eyes, and focus, also known as accommodation. Both of these mechanisms are crucial in stereoscopic vision. Vergence or independent inward/outward rotation of eyes is engaged to fixate on objects and perceive them as single. Incorrect vergence response can cause double vision. Accommodation is the eye’s focusing mechanism and it is engaged to produce a sharp image on a retina. Both of these mechanisms are neurally linked forming the accommodation-convergence reflex<ref>{{Cite web |title=Reflex action {{!}} Definition, Types and Mechanism and Important solved questions |date=11 November 2020 |url=https://www.crackyourtarget.com/reflex-action.html}}</ref> of eyes. One can distinguish vergence {{nowrap|distance{{px2}}{{mdash}}{{px2}}}}a distance of a point towards which both eyes are converging, and an accommodation {{nowrap|distance{{px2}}{{mdash}}{{px2}}}}a distance of a region in space towards which the focus or refractive power of the crystalline lens has been adjusted to produce a sharp image on the retina.

==Causes==

==Causes==

===Virtual and augmented reality===

===Virtual and augmented reality===

Examples of fixed-focus biscopic devices that can cause focal conflict include the [[Oculus Quest 2]], [[HTC Vive]], [[Valve Index]] and the [[Microsoft HoloLens]]. Focal conflict can be experienced by bringing a virtual object very close to one's eyes in the headset and trying to focus on it.<ref>{{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=2022-09-22|publisher=VR Trailers & Clips|date =18 July 2020| via=YouTube|format=Video}}</ref>

Examples of fixed-focus biscopic devices that can cause focus conflict include the [[Oculus Quest 2]], [[HTC Vive]], [[Valve Index]] and the [[Microsoft HoloLens]]. Focus conflict can be experienced by bringing a virtual object very close to one's eyes in the headset and trying to focus on it.<ref>{{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=2022-09-22|publisher=VR Trailers & Clips|date =18 July 2020| via=YouTube|format=Video}}</ref>

Stereoscopic displays such as [[holographic display]]s and [[light field display]]s can remove the problem.<ref name="kramida" />

Stereoscopic displays such as [[holographic display]]s and [[light field display]]s can remove the problem.<ref name="kramida" />

===Other causes===

===Other causes===

Focal conflict can be experienced when using other technologies, including:

Focus conflict can be experienced when using other technologies, including:

*when viewing a [[stereoscopy|stereogram]] through a [[stereoscope]]{{citation needed|date=September 2022}}

*when viewing a [[stereoscopy|stereogram]] through a [[stereoscope]]{{citation needed|date=September 2022}}

*when viewing an [[autostereogram]] using an eye defocusing technique{{citation needed|date=September 2022}}

*when viewing an [[autostereogram]] using an eye defocusing technique{{citation needed|date=September 2022}}

==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 focus 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>

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, [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].    

Multifocal displays are a way of overcoming focal conflict. The principle of operation relies on availability of multiple image focal planes (screens), which from the perspective of a viewer are available simultaneously at all times. This gives the ability to accommodate eyes within the available range of focal distances and perceive realistic monocular focus (image blur) cues similarly to natural viewing conditions. Essentially multifocal displays discretize the depth dimension and split or slice the 3D content according to the available configuration of depth planes to minimize focal conflict. The topic of multifocal displays has been generously researched for at least several [http://bankslab.berkeley.edu/publications/Files/stereo_display_prototype04.pdf decades],<ref>{{Cite journal |last1=MacKenzie |first1=Kevin J. |last2=Hoffman |first2=David M. |last3=Watt |first3=Simon J. |date=2010-07-01 |title=Accommodation to multiple‐focal‐plane displays: Implications for improving stereoscopic displays and for accommodation control |url=https://jov.arvojournals.org/article.aspx?articleid=2191682 |journal=Journal of Vision |language=en |volume=10 |issue=8 |pages=22 |doi=10.1167/10.8.22 |pmid=20884597 |issn=1534-7362|doi-access=free }}</ref><ref>{{Cite journal |doi=10.1364/AO.39.003209 |title=Multifocal planes head-mounted displays |year=2000 |last1=Rolland |first1=Jannick P. |last2=Krueger |first2=Myron W. |last3=Goon |first3=Alexei |journal=Applied Optics |volume=39 |issue=19 |pages=3209–3215 |pmid=18349886 |bibcode=2000ApOpt..39.3209R |s2cid=16434842 }}</ref> nevertheless, there is only a limited offering of commercially available [https://lightspace3d.com/ multifocal] near-eye displays.

Multifocal displays are a way of overcoming focus conflict. The principle of operation relies on availability of multiple image focal planes (screens), which from the perspective of a viewer are available simultaneously at all times. This gives the ability to accommodate eyes within the available range of focal distances and perceive realistic monocular focus (image blur) cues similarly to natural viewing conditions. Essentially multifocal displays discretize the depth dimension and split or slice the 3D content according to the available configuration of depth planes to minimize focus conflict. The topic of multifocal displays has been generously researched for at least several [http://bankslab.berkeley.edu/publications/Files/stereo_display_prototype04.pdf decades],<ref>{{Cite journal |last1=MacKenzie |first1=Kevin J. |last2=Hoffman |first2=David M. |last3=Watt |first3=Simon J. |date=2010-07-01 |title=Accommodation to multiple‐focal‐plane displays: Implications for improving stereoscopic displays and for accommodation control |url=https://jov.arvojournals.org/article.aspx?articleid=2191682 |journal=Journal of Vision |language=en |volume=10 |issue=8 |pages=22 |doi=10.1167/10.8.22 |pmid=20884597 |issn=1534-7362|doi-access=free }}</ref><ref>{{Cite journal |doi=10.1364/AO.39.003209 |title=Multifocal planes head-mounted displays |year=2000 |last1=Rolland |first1=Jannick P. |last2=Krueger |first2=Myron W. |last3=Goon |first3=Alexei |journal=Applied Optics |volume=39 |issue=19 |pages=3209–3215 |pmid=18349886 |bibcode=2000ApOpt..39.3209R |s2cid=16434842 }}</ref> nevertheless, there is only a limited offering of commercially available [https://lightspace3d.com/ multifocal] near-eye displays.

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

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