Why Do Curved Sunglasses Lack Power Despite Their Design?

[Aronyak]

Please someone tell me why sun glasses have no power,though they are curved...

 

[CWatters]

They do very slightly distort light but because both surfaces are curved and parallel and the material thin the effect is minimal. Like looking through a window.

 

[Vanadium 50]

You can get prescription sunglasses, which do have 'power'.

 

[sophiecentaur]

A lens works because of a difference in curvature between the sides. A curved sheet of glass with parallel sides is neither concave nor convex and does not act as a lens. This statement only really applies for relatively thin glass that isn't 'very' curved. Extremely thick / curved glass sheets will distort images, although they don't behave like simple lenses either.