the letters on the glasses lens are mainly used to indicate the brand and type of the lens, and are also used as anti-counterfeiting marks. These letters usually contain the following information:

1. Brand name or trademark: Some lens brands will print their own brand names or trademarks on their lenses to show their brand identity and quality assurance.

2. lens type: some lenses will be printed with specific type symbols, such as "progressive" on progressive multifocal lenses and "color change" on color-changing lenses.

3. lens parameters: some lenses will print some parameter information, such as lens degree, sphericity, pupil distance and so on.

4. Anti-counterfeiting marks: Some lenses will also add special anti-counterfeiting marks on the lenses to prevent the appearance of counterfeit and shoddy products. These anti-counterfeiting marks are usually only visible under certain conditions, such as in the case of fog.

In short, the letters on the glasses lens are used to identify the brand, type and specific parameters of the lens, and can also be used as anti-counterfeiting marks.