You have to be calm when the resident screws up, because the pt is usually awake and alert during eye surgery. Anything you say (and the way you say it) will impact the pt's state of mind (and the last thing you want is a panicky pt!)
Speaking of speaking during eye surgery...When I was a first-year resident, I was assisting the attending while he performed a corneal transplant--he was 'throwing' sutures, and I was cutting the tails after he tied them off. At one point, I cut the tails too long, and without thinking said "Oops." The attending leaned back from the microscope, looked at me like I was an idiot, and said, "Don't say 'oops.'" I immediately took his point.