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Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies (eye focusing). For distant vision, the ciliary muscle must relax and the eye’s crystalline lens is stretched out.

When using a Virtual Reality Device (Occulus Rift, Samsung VR, Sony VR, Google Cardboard etc.) the eye has to focus on the screen that is only a few centimeters away from the eyes. I am aware of the Vergence-Accommodation Conflict. Yet I ask myself,

Is the ciliary muscle relaxed or contracted when looking at a (virtually) far distant object projected on the LCD of the VR-Device?

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The eyes cannot focus on something a few centimeters away. The average maximum distance where the eye can still focus is 14 Diopters in young people (Duane, 1922) (approximately 7 cm in 8-year olds). The distance to the eyes of the display in a head-mounted display (HMD) is often less than this and hence the eyes cannot possibly focus on this. Instead, with the use of lenses, a virtual image is created at a virtual distance approximately a meter away (Fig. 1). In the Oculus Rift DK1, for example, the virtual screens were infinitely far away; in the Oculus Rift DK2, they are about 4.5 feet (1.4m) away (source: Immersive Computer Graphics). One meters is a comfortable viewing distance with minimal accommodation needed and hence little eye strain (source: Immersive Computer Graphics). At around 6 meters the eye is unaccommodated.

HMD lens
Fig. 1. Virtual image in a HMD. Left: eye failing to focus on a very close real screen. Right: eye able to focus on the virtual image of the same real screen created by an interposed lens. source: Immersive Computer Graphics

Reference
- Duane, Trans Am Ophthalmol Soc (1922); 20: 132–57

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  • $\begingroup$ Did you notice that the image you've posted gives an optical illusion when scrolling page up/down?! Or is it just me? ;) $\endgroup$ – another 'Homo sapien' Apr 21 '16 at 10:32
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    $\begingroup$ @another'Homosapien' - wow! I hadn't noticed :D $\endgroup$ – AliceD Apr 21 '16 at 11:00

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