Can clear plastic lenses in glasses get tinted from too much exposure to heat?

I have an old pair of glasses that are now my backup pair. They stay in my car's glovebox all of the time. They have been in there nonstop for almost 4 years now. Today I tried them on and they seem to be very slightly tinted now. They are not the kind that change tinting according to the light. They are just normal clear plastic lenses. I don't remember but they might have UV protection also. Could all the hours of heat exposure in my car have caused some sort of tinting?Can clear plastic lenses in glasses get tinted from too much exposure to heat?
All plastics change clarity over time.Can clear plastic lenses in glasses get tinted from too much exposure to heat?
err! no