Glass eye I'm not sure about either. That seems along the lines of using a fingerprint reader on a prosthetic hand. Sure, you could mold a fingerprint onto one and scan it, but with a sophisticated fingerprint sensor it's going to look like a fake finger. Do we deliberately make everyone's fingerprint scanner weak to allow someone without fingers to use it?

Maybe the answer is to introduce a "weak mode" option where most users could have the scanner verify "yes, this is a real eyeball," and if someone with a glass eye still wanted to use iris scanning in a way that can be copied by a photo, they have the choice to disable the security measures.