This is a link to a blog that has some of the best analytical and useful technical data on understanding the nuances of how Lenses, Optics and Displays impact the implementation of VR HMDs. There’s are lots of useful articles in his blog and if you’re looking to understand better some of the technical and engineering aspects of VR, I highly recommend you check it out.
In the latest post, he describes a nice systematic way of measuring the effective resolution of HMDs and trying to remove as much perceptual bias as possible.
Link here: http://doc-ok.org/?p=1631
VRomit's World 