Relaxing Eyes when using Virtual-Reality-Glasses?
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.


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