In most cases, it depends on the eye exam you have. In other words, you need to get new pairs when your optometrist recommends you to do that. This usually occurs in the same time when you have your regular eye exam. Non-senior adults and children over 6 have regular eye exams a minimum of once every two years if they do not have risk factors for poor vision. The adult over 60 with risk factors should have an eye exam every year or more frequently if you recommended by their doctor. During this regular eye exam, you will need to ask your optometrist whether or not you need to replace your glasses with a new pair. Be sure to bring your old glasses with you so that your eye doctor can inspect them for flaws and durability.