Thanks Gozu for your answer.
Yes i tried the r.SetRes 2160x1200 and also the loading of a new level as mentioned in other posts but it does not fix anything.
So i did some tests with the VR title that i own and the conclusion is that right now the unreal engine VR games are much more blurry than the unity game.
I even found that Nvidia fun house is blurry compare to the Lab from Valve.
It seems that the problem comes from the way anti aliasing is handle.
I found this post and i could not agree more with it : Does Epic Have a Proper Solution for Anti-Aliasing in VR? - VR and AR Development - Unreal Engine Forums
I also found this article from the occulus team that explain they had to modify the unreal renderer in order to get sharper image https://developer.oculus.com/blog/introducing-the-oculus-unreal-renderer/
So right now it seems that we are waiting for an upgrade for the unreal engine in order to adress this issue.