Microsoft Research has developed an improved Lens design for Oculus Rift HMD. They have released CAD files and source code necessary to build and use an improved lens for the Oculus Rift HMD.
The source code works with the Unity game engine to correct the lens distortion for the Oculus display. The lens was automatically designed by the LensFactory program developed at Microsoft Research. The optical quality is significantly better than the lenses that come with the Oculus. The lens uses off the shelf lens elements from Edmund Optics.
Download it from the link below.