After Boethiah tells me to go kill those guys at Knifepoint, the visual effect doesn't go away. I read from the wiki that loading a previous save would fix that, but all my saves are after the bug. Is there some other way to fix this ? A console command maybe ?

what 'visual' bug? do you get the full conversation from her after sacrificing your follower? if not try:

setstage DA02 15

or

setstage DA02 20

here's the known bugs: http://www.uesp.net/wiki/Skyrim:Boethiah%27s_Calling#Bugs i had the one where the dragon showed up when i was going there to sacrifice the follower. the console command advanced it.

edit - oh, the state you are in when you talk to her? try the setstage DA02 20 and see if that clears it up.

CLICKY. That always makes me laugh.

Yes, the weird blurry state, when you are talking to her, everything else seems fine. Talked to her, killed the cultists, off to the kinfepoint, but I still see everything weird. Your advice on setstage DA02 20 didn't help. Anything else ?

The UESP link you gave me doesn't list this as a bug. The other one does, It's the third bug in the list.
http://elderscrolls.wikia.com/wiki/Boethiah%27s_Calling

Anyone ? I need to play skyrim, but I can't like this. Btw, I think in my case, the bug was triggered when I looted the dead cultist's bodies, not watching my journal, as it is said in the wikia.

Well, I managed to fix it. All I had to do is finish the quest, after talking to Boethiah again in the end, the stupid tunnel effect vision stopped and everything is back to normal.