If AI glasses are a problem during exams and hard to monitor, shouldn't they just ban horn-rimmed glasses from the start?

Since AI glasses have to be made of plastic, it would be difficult to use metal frames.
Couldn't they just prohibit horn-rimmed glasses and only allow metal frames?
‌People who actually wear glasses usually have spare pairs,
and don't they also own glasses that aren't horn-rimmed?
If not, glasses aren't that expensive, so they could just get a pair specifically for exams.
If there is no way to distinguish them, I feel like they should just ban horn-rimmed glasses.