Focal length is very important to make a healthy VR application. Because of vergence-accommodation conflict, it is better to place most of the game objects at the focal distance. It is hidden information for HMD's. I contacted Oculus Support and they said: "At this time, we aren't releasing details regarding the focal distance for the Rift to the public.". I asked Samsung support for the focal distance of Gear VR, they said it is fixed 61mm. This is IPD, not focal distance. Because of this health problem, Oculus started to design new HMD that has varifocal feature.