This is defined as a painful Zenith Lab Vision 20 sunburn of the eye that causes the symptom of temporary vision loss for a period of 2 days and Pterygiums which is described as a growth of tissue around the edge of the cornea that can only be corrected by surgical removal. Sunglasses should be worn regardless of weather conditions as the potential dangers of U.V rays are ever present in sunny weather and also cloudy weather.
In terms of choosing the right pair, it's important to ensure that they block 100% of U.V rays of the sun. An ideal pair of sunglasses that provide maximum protection from the sun would be a pair of sunglasses with the ANSI label on it. ANSI stands for the American National Standards Institute. It is a common misconception that the darker the shade of the sunglasses, the greater the protection.
In fact, wearing a darker shade defeats the purpose of your sunglasses because they cause the pupils to dilate, causing more U.V rays to enter the eyes. It is not the shade of darkness that matters but it is the coating on the lenses that makes them safe. Store bought sunglasses are more reliable than those purchased from a street vendor.