Polycarbonate lenses the lenses are made in 2mm polycarbonate a material offering first rate optical features excellent impact resistance and extraordinary lightness it has a low refraction index and does not let ultraviolet rays filter through all polycarbonate lenses are subjected to surface hardening treatments that make them resistant to abrasions and solvents off center lens northwave glasses have lenses with an off center base the axis of the focal centre is aligned with the focal c