How to add blur to screen [like blurry vision]

hello everyone:

how do you add different degree of blur to the screen so that everything on the screen appears slightly blurry or super-blurry depending of game variables you can control at run time?

i played around with webgl effects with no luck. i dont want a glassy-glossy overlay look, i also dont want a "water" effect (waving back and forth as if an object is under the water) but a plain simply blur.

any ideas how i can do that?