What do you know about invisible bifocal glasses?

[classic frames]

It was a week ago that I found my eyes also had problem with near vision, the doctor suggested me to try bifocal eyeglasses, but when I was ordering such eyeglasses online yesterday, choosing the lenses, there was an “invisible” option, have you ever heard about invisible bifocal eyeglasses? I just want to know what the difference between invisible eyeglasses and ordinary eyeglasses is.