If one`s prescription value is high,the eye optometrist will ask you whether prescribe aspheric lenses or spheric lenses .Generally,aspheric eyeglass lenses are thin.Because advanced optical desigh technology allows aspheric eyeglass lenses to be made with flatter curves than conventional lenses,and the profile will be more slimmer and more attractive.Also that`s why aspehric lenses sell much more expensive than spheric lenses.