When you ride your bike, no matter if you are amateur or a professional, sunglasses are necessary. The most obvious reason why a cyclist should always wear sunglasses (i.e. to protect your eyes and ride without problems also when the sun is in front of you) is not the only one, though! The best cycling glasses also have other functions, and to accomplish these objectives they need to have specific peculiarities.
In order to fully understand why glasses are so important for cyclists, just think about what happens when you ride your bike: you often reach high speed and get lashings of air on your eyes and face. In this case glasses can be compared to a windscreen for our eyes, which protects you from wind. Just like the windscreen of a car, moreover, sunglasses protect our eyes also from little insects and pebbles, dust and other foreign bodies that might get into your eyes and cause problems that might be dangerous.
The protective function of sunglasses does not limit to sun and light, it is more complex than that. As far as sun and lights are concerned, moreover, sunglasses do not only protect your eyes from UV rays: each cyclist knows well that during a race, a training session or a simple ride, there can be fast changes from light to shade, dazzling, glares and so on. All these things are not only a source of stress for your eyes, they can also put at risk your safety, distracting you and limiting your visibility. This is why professional glasses can really help you!