When you are delivering a PowerPoint presentation, 90 to 95% of the time you should be looking directly at individual audience members. You're looking at the screen, it means you didn't prepare means either you have awful slides or you didn't prepare the right way or you didn't have notes structure the right way. And you're practically inviting your audience to fall asleep or check their email. You need to be looking at them to see are they getting it? Does it make sense they look confused. They have a question you need to be reading your audience at all times, so your eyes should be focused on your audience, not your slides and certainly not reading a full script.

Find a glance down occasionally, at a single sheet of notes.