My girlfriend told me that she wanted to buy a pair of transition prescription sunglasses. she asked me to choose one for her. but I didnít have this kind of sunglasses before and have no idea about transition prescription sunglasses. this is my first time to hear of it. Who can tell me what is the transition prescription sunglasses and whatís the difference between common prescription sunglasses and transition prescription sunglasses? and what is its action? Thank you for any help!!