Casual is for everyday use and blocking the sun while doing normal activities. Sports sunglasses are specifically engineered for running, biking and other sports activities. Glacier is highly advanced to protect your eyes from the glare off of snow which can be quite intense. If you know you partake in each of these activities extensively, it doesn't hurt to get more than one pair of sunglasses--while it may be pricier at first, you will find that you will get the most life out of your sunglasses this way.