Sources:
https://www.aoa.org/Documents/optometric-staff/Articles/Frame-Materials.pdf
https://www.forbes.com/sites/anaswanson/2014/09/10/meet-the-four-eyed-eight-tentacled-monopoly-that-is-making-your-glasses-so-expensive/#33a99ace6b66
https://en.wikipedia.org/wiki/Luxottica
https://eyeglass.com/shop-by-brand/criss-optical.html
https://en.wikipedia.org/wiki/GI_glasses
https://www.google.com/search?hl=en&biw=2526&bih=1281&tbm=isch&sa=1&ei=KWnHW6DNEJCB8APngquYCw&q=criss+optical&oq=criss+optical&gs_l=img.12...0.0..11259805...0.0..0.0.0.......1......gws-wiz-img.N_8JmbZNnKM
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