my prescription is very strong, -16.00 OD and -12.50 OS, the online customer service of eyeglasses shop tells that it is not workable with frame NN1163 I originally selected. They strongly recommend me choose a small and suitable frame PN1077, also, the lens is Biconcave. The shape is concave on both faces of lens. It is too thinner at the middle of lens, and the vision field of lens is much large. But, my eyes may be looked too small via these lenses while other people see me.