Synopsis
Throughout the first two parts almost everything we see is through the eye of the camera (designated in the script as E), although there are occasional moments when we see O's perception. In the third part we get much more of O’s perception of the room and its contents. In order to distinguish between the two perceptions, objects seen by O were shot through a lens-gauze, blurring his perception while E's perception was shot without gauze or filters, keeping the images sharp.
Read more about this topic: Film (film)