As a check on the quality of eye glasses purchased over the internet, glasses were individually ordered from several different online vendors. Among the 92 lenses with antireflection coating, 61 prescriptions required a thickness at the center greater than \(1.9 \mathrm{~mm}\) and 31 were thinner. Of the 61 thicker lenses, 12 failed impact testing while 18 of the 31 thinner lens failed.