Marking of lenses

In a method for marking plastic lenses composed of polymethyl methacrylate which comprises:

• passing a laser beam through a mask having selected openings permitting the passage of the beam, said mask being composed of a material impervious to laser beams, and
• passing the selected laser beam through a focussing lens to focus said beam onto the plastic lens retained in a holder, said focussing lens being composed of material which will trasmit infrared radiation in the 10.6 micron range, the improvement wherein said plastic lens is held in a holder comprising a cylindrical body portion and a plurality of prongs extending upwardly therefrom, each prong having an inner ledge set at a predetermined height above the top surface of the body portion, and an upwardly projecting wall beyond the ledge, said wall being slanted outwardly to the top portion of the prong.