Although not all scientists agree, there is some research that suggests an association with daily exposure to UVB in very bright sunlight over a period of many years. UVA rays are mostly absorbed within the lens of the human eye. While there are no documented disorders of the human eye from UVA, it remains a much studied and debated topic. As a result, sunglass standards place limits on UVB and UVA for sunglass lenses. The small amount of pupil dilation in the eye, due to the wearing of sunglasses, is not known to cause any problems.
All sunglasses absorb UV more strongly than visible light.
Therefore, sunglasses actually provide substantially more UV reduction than the shade. Wearing a pair of sunglasses does not increase your exposure to UV radiation nor does standing in the shade. Under bright conditions sunglasses are very helpful to drivers to reduce the brightness and glare, thereby allowing better vision under those driving conditions. Sunglasses should not be worn at night. They are not meant to be worn after dark.