Thank you.
I have actually found lightly tinted glasses that are comfortable, and work very well for me.
Part of the problem is that there are "James Bond" Internet access glasses that allow one to covertly access the Internet for the purposes of cheating and academic dishonesty.
Internet-connected glasses
So--as a consequence--sunglasses are not allowed in class. Just keep in mind that this is something I assume from offhand comments that I've overheard, and I don't know if this is a specific college policy.
I have gotten very angry (at a prior school) when an albino student (my study partner, actually) was allowed to wear dark glasses, but I wasn't . . . as I didn't have a "medical need."
Part of the other reason why sunglasses and visors are a problem probably has to do with drug abuse. Professors don't want a chemistry student (for example) handling Bunsen burners, flammable liquids, and corrosive acids while they are under the influence of substances . . . for obvious safety reasons.
There are people who seem able to tell if someone is doing drugs just by looking in their eyes and--as a paramedic--I count myself in this category, as nystagmus (a type of eye movement) and pupil dilation are indicators of drug use, and I've been trained to evaluate these signs when assessing a patient.