12 a and 12 b are known as wraparound lenses and typically have a small radius of curvature which is known in the industry as a u201c base 8 u201d curvature such lenses are typically non prescription lenses and may be tinted so as to reduce glare under different types of lighting conditions as shown in fig2 the lenses 12 a and 12 b are selectively replaceable in the frame 8 on each side of the frame 8 there is a channel 16 a 16 b and the lenses 12 a and 12 b each have an upper edge 18 a 18 b that cooperatively fits into the respective channels 16 a and 16 b to help retain the lenses in the channels the lenses have tabs 19 at each end that mate with correspondingly shaped portions of the channels 16 a and 16 b referring to fig4 the frame 8 is now fitted with lenses 13 a and 13 b having a larger radius of curvature conventionally know as u201c base 6 u201d curvature for example prescription lenses because of the requirements for thicknesses in certain prescriptions are thicker than tinted sports lenses such as the lenses 12 a and 12 b and cannot easily be made with base 8 curvature to do so requires an expensive process that may make the cost of such lenses prohibitive the frame 8 is designed for a semi rimless configuration which means that the bottom edges and.