If you have eye problems,such as dry eyes or strain,designer glasses can do nothing about it.If you refer to the nearsightedness or farsightedness, designer glasses can't correct your vision better than the ordinary ones do. But what inferior to cheap glasses are their quality, brand image and the design.
A lot of cheap sunglasses are fake products, which are made of poor lenses and provide barely UV protection and a clear vision. On the other hand, designer sunglasses , though very costly, provide great appearance as well as great lenses that would provide great UV protection and better protect our vision. The key is their difference is the lenses.