Why do my glasses have numbers on the lenses?
There are little markings on the lenses to allow the optometrist/dispensing optician to 'mark up' the lenses to check positioning. The numbers may be visible on bifocal lenses. Bifocals require different positioning for different visions. But the number may not noticeable on the progressive lenses. Only a couple of types of lens are marked in this way, and others are safety glasses.