The lenses in your sunglasses are the most critical part of your purchase. The lenses can range from basic injected plastic lenses to specialised glass lenses with various technical qualities. At the lower end the of lenses you will probably find a primary plastic lens, which will protect your eyes from UV rays as well as reduce brightness due to the tint applied to them. The degree of UV protection from the very cheap sunglass lenses is usually not sufficient. As you travel up the price ladder, the lenses will have specific qualities, that make wearing them more comfortable. They will be more durable and suited to particular conditions and tasks. These lenses are usually the result of intense research and development.