Aspheric lenses are generally used in high prescription cases. It can be used in both high plus and high minus lenses but the thinning effect is most noticeable for people with a high plus prescription. In aspheric lenses the curvature of the lens is changed which makes the lens thinner and also reduces or eliminates lens distortion or aberration. What this means is that the Rx is more likely to be clear across the breadth of the lens. In summation, a thinner and clearer lens is what an aspheric lens is.