Everything has two sides. So do sunglasses. On one hand, sunglasses are widely recommended by eye doctors and professionals to gain protection from UV radiation in sunlight. Using sunglasses as much as possible especially in younger days is commonly believed to avoid certain age-related eye problems including cataracts. However, on the other hand there are still good reasons to discard sunglasses. The most outstanding example for the latter side may be the American ophthalmologist called Dr. Bates who insisted that sun was quite beneficial for the eyes. There were a lot of cases that he advised his patients with light-sensitivity to expose their eyes to the bright sun rays and finally cured this problem. Exercising this thought in clinical practice, he even strongly dissuaded his patients from wearing sunglasses.
Many people may have the experience that they noticed tired eyes after being in a shopping box such as Wal-Mart and got almost a burst of pain in the eye when they went out into the sun. Most of them in this situation would put on sunglasses in order to block the fierce sunlight. However, the right action is to look at the sun but keep the eyes closed. The feeling is actually caused by the awful fluorescent light and complete lack of day light. Most people will not deny that their vision in a bright sunlight is better than that in a dark environment. By exposing to sunlight, the eyes can get quick refreshed.
The fundamental principle is that the eyes are organs that are designed for light. Dating back to the beginning of human civilization, all human beings were used to deal with the natural sun light. No one in those days wore sunglasses. Another testimony is that all infants need light simulation to acquire visual skills that are simplest possible. Modern types of sunglasses are always designed to diminish the natural flow of sunlight to the wearers' eyes. In particular, dark prescription eyeglasses that stay constantly on the face are especially not encouraged.