I think both 1.59 Polycarbonate lens or 1.61 Thin Light Edidon Lens is OK for -5.50 eyeglasses. Of course, they are different for making the eyeglasses. Polycarbonate lenses (PC lenses) are 10 times more impact-resistant, lighter and thinner than normal plastic lenses (Resin lenses). They can also offer 100 percent UV protection and scratch protection. And 1.61 Thin Light Lens are the high index lenses that suit for people have strong eye power.