CR-39 lens, which is a type of plastic, is the most popular type of lens due to its low cost, light weight, and yet high optical quality. In terms of optical quality, it ranks below Polycarbonate lens, but above high-index lens.
Also known as Multifocal, progressive lenses provide a smooth transition from near correction to distance correction while eliminating segment lines that are present in bifocal lenses. Those who are prescribed bifocal glasses, can use progressive glasses instead, and vice versa.
If your prescription does not mention progressive or bifocal, this is the type of lens you will need. This type of lens corrects for one distance, as opposed to bifocal or progressive lenses that allow for both distance and near vision. If your lens mentions "progressive" or "bifocal", you cannot use this type of lens instead.