Recently, I purchased a pair of glasses from a privately owned optic store. I specifically asked for hi-index lens (1.56 or 1.60, I am not sure). The lens I got, however, is kind of thick (around 5 mm thick on the edges).My eye -sight is poor though, -5.00 sphere, -1.25 cylinder on the worst eye. Are there ways to tell if the lens is high-index or just plain regular lens, besides the thickness? Also, there are "rings" on the edge when I look parallel to the surface of the lens.