Changes

== 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-focal conflict.

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]] (inverse of meters). Hence the difference between the reciprocal of the vergence distance and the reciprocal of the focus distance characterizes the extent of vergence-focal 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-focal 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-focal conflict for a person with normal vision would be 3.33-0.5=2.83 diopters.