Pupillary distance or interpupillary distance (IPD) is the distance measured in millimeters between the centers of the pupils of the eyes. Everyone is different and the value changes based on whether you’re looking at something close up or far away. But why does this matter to the virtual reality participant?
Even if you’re not into virtual reality, you may be familiar with IPD as it is important in the positioning of the lenses in your eyeglasses.
The optical center of the lenses must be positioned correctly in relation to the center of your pupils or undesired results can ensue; such as eye fatigue and headaches.
The further your eyes shift from the optical center of the lens, the more the light hitting your retinas is going to be bent in various ways that aren’t going to be “right” — and this is what causes the aforementioned issues.
What’s even more crazy is that when you’re looking at something far away your IPD is greater than when you’re focused on something closer; your IPD is dynamic by a couple of millimeters.
Now that we have an idea what it is (a variable distance different on everyone) and why it matters (your well being!) — let’s apply this to virtual reality.
Much like your eyeglasses or even binoculars, each eye is looking through a separate lens. Your optometrist takes care of your glasses and quality binoculars actually allow you to adjust that distance between them.
You would rightly assume that all virtual reality systems out there would allow you to adjust the lenses to match the wearer’s IPD.
… and you would be wrong.
Amazingly, popular VR headsets like the Oculus Rift S and the recently-departed GearVR do not have hardware-based IPD adjustment solutions — meaning there is not a little slider or knob you can manipulate to move the lenses closer together or farther apart. Many WMR headsets also suffer this omission.
In some cases, the virtual reality device promises “soft IPD adjustment” — where the screens themselves are offset when…