Try to open in notepad file called game.cfg (in Amnesia/redist/config).
There are several values. Try to change few:
<Player_General
FlashbackRadialBlurSize = "0.09" // to "0.0"
FlashbackRadialBlurStartDist = "0.3" // to "0.0"
<Player_Sanity
NearEnemyDecrease = "0.3" // to "0.0"
There are much more about darkness, enemies, critters, increasing and decreasing values. Yet, I still cannot remove blur vision completely by this; perhaps someone else will find solution
EDIT
Oh right, I think I resolve this so far. Just delete shader called
posteffect_radial_blur_frag.glsl in Amnesia/redist/core/shaders. Don't forget to make back up of this file!! Blurring effect is remove completely. I notice no issues so far (but be careful).