I think Global Entry is one of the greatest things the United States government ever did (along with TSA Precheck). I love being able to enter the county quickly and move on to a connecting flight if I have one.
I almost made a big mistake when I last entered the country a few weeks ago in Tampa. I wore my glasses.
I went to the kiosk and it took my photo quickly and then said I had to go see an agent. That agent said the kiosk couldn't scan my eyes because of my glasses.
He said this was my warning and the next time, I would have to go into the regular line for immigration.
So even though there are no signs on the kiosk or in the line for the kiosk saying not to wear glasses, take it from me. Don't wear glasses as you go up to the Global Entry kiosk or you might find yourself having to go into the regular line.