Is flying without sunglasses in daylight doable in a Cessna 172? Do the windows in a 172 provide any protection from the sun or is too bright? Particularly, if one wants to do a flying lesson and was told to bring sunglasses more than once.  So, is it critical?  My friend doesn't have sunglasses and would have to get prescribed ones which he can't get now. He got a gift of a flying lesson so he wants to try it but is being in the plane without sunglasses doable?  Or will he be squinting the entire time? Or is it really bad for your eyes?
Definitely doable. No real protection from the sun just through the windshield but I flew a C172 for many years only using sunglasses occasionally. Just don't make the same mistake I did when I first started flying- paid a lot for a pair of polarised sunglasses then jumped in the cockpit and all the LCD screens went blank! :)