Galaxy Note 7's iris scanner won't play nice with glasses
A breakdown from TechTastic says that the phone seems to give a warning that the iris scanning feature may not work on people who wear glasses. Meanwhile, those with contact lenses may not be able to use it in a low-light setting.
For everyone else, there’s a sweet spot to hold the device to get the iris scanner to work. Holding your phone any closer than 20cm from your eyes will most likely result in an error. It’s advised that you hold it between 25cm and 35cm away.

