Vergence-Accommodation Conflict

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Our eyes use depth cues and light to properly look at objects. Vergence is when the eyes rotate, and accommodation is when the eyes adjust their focus. The brain expects these two mechanisms to be linked.

In a VR headset, depth cues and light aren’t always linked. Current headsets have fixed focal lengths, 1.3 meters for the Quest 2 for example. This means that any objects at that focal length or beyond will be displayed mostly accurately, but anything closer will get blurry and sends confusing signals to our eyes. Our eyes will use depth cues to converge on the close object, but still be getting light signals from the screen telling it to accommodate to a 1.3 meters away or greater object. This is the VAC, and the confusing signals cause eye strain.

Our eyes can account for the VAC, especially for people experienced with VR, but over time the conflict will always cause eye strain. Until VR technology advances, there are important design guidelines to follow:

Anything closer than around 1.5 meters should be temporary or not require extended focus

Moving objects should move slowly, and ideally move short distances and be far from the user. It takes the eyes some effort to refocus on objects at different distances away, and the VAC makes this harder

Note: the Quest 3 does not solve this conflict, nor will the Apple Vision Pro since users need to get a custom presciption for it [48] which means that the lenses have a fixed focus.

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