Great surgeons take utmost care of even the smallest of the details.
It starts right from the slit lamp examination.
In the OT, the first step is draping of the eye.
Poor draping is not only unsafe in the sense that it can lead to post op infections but can also lead to great discomfort and hindrance while operating.
Here is a link to a video that shows how meticulous draping must be done before the surgery.
Not that something must be placed over the patients nose so that he or she does not experience that feeling of suffocation more so if the patient suffers from COPD or cardiac ailments.