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Firstly, if I ask this question in Ask Different or Super User, the users there may say this is related to a biology or physics.

The background is: we were in general told that: don't read a book too close, or don't watch the TV too close, because it will make our eyes focus with a really short focal length, and that means our eye muscle has to make the biological lens in our eyes to be extremely convex shaped. As a result, we can easily develop myopia this way.

Does this apply to VR headsets, such as Apple's Vision Pro, or Meta's Quest 3? In these cases, the "display" is like one or two centimeters or fractions of an inch away from our eyes.

So in that case, does that make our focal length to be extremely short and therefore, injure our eyes in the long term?

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The VR headset is presenting two different images to each eye, so strictly speaking, the eyes are not looking at the same object (as in a book or TV).

This idea has been used in non electronic devices (Stereoscope) for a long time to see pictures in 3D.

So the eyes are not actually focusing at the VR device screen but further away.

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    $\begingroup$ I don't think it works this way: Mom says: hey Peter, don't watch TV so close, like 2 feet away. Peter says: Mom, don't worry, I am closing one eye to watch the TV 2 feet away, so it is not using two eyes and so it doesn't matter $\endgroup$ Commented Feb 29 at 6:13
  • $\begingroup$ @heracho its about distance to the screen from the eye $\endgroup$ Commented Feb 29 at 17:06
  • $\begingroup$ So, your question is more about this phenomena? : en.wikipedia.org/wiki/Vergence-accommodation_conflict $\endgroup$
    – heracho
    Commented Feb 29 at 18:32
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The display may be two centimetres away, but there are lenses between the display and the eyes, and they project the image to make it look like it is much further way. This is necessary, because most people cannot focus properly on an object that is only 2 cm away, and it would cause the eye strain or fatigue that you mention.

It's a bit like looking through prescription glasses. Lens are very close to our eyes, but it is not the lenses that we focus on. We focus on where the light rays coming through the lenses appear to be coming from.

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