Every pair of prescription eyeglasses begins with a piece of glass or plastic called a lens blank. Making a pair of optical lenses is a precise and complex job done by skilled opticians. The work is done in a lens laboratory that uses specialized machinery to cut, shape and polish a lens based on a doctor's specifications for an eyeglass prescription.
Lens Blanks
The basis of all prescription eyeglasses, lens blanks are available in many styles and materials including glass, plastic, polycarbonate, hi-index and different types of single vision and bifocal lenses, as well as different colors and coatings. According to the opticianworks.com website, optical labs must stock thousands of types of lens blanks to be able to make custom prescription lenses.
Surfacing
Surfacing is the process of grinding the lens blank down and putting curves into the lens that make the prescription. During the surfacing process, the lens blank is covered with a thin film to protect it from extreme heat. The film keeps the lens from being damaged and also helps the lens block, the piece that holds the lens in place, adhere to the lens during surfacing. A diamond edge cutting tool inside the surfacing machine cuts and shapes the surface of the lens blank to the detailed prescription information. The lens is smoothed and polished to make it clear.
Finishing
Finishing is the process in an optical laboratory that shapes a processed lens blank to fit into a specific eyeglass frame. The lens blank is put into a machine with a matching pattern from the frame and the machine uses an abrasive wheel to cut and edge the lens blank to the exact size of the pattern.
Beveling
Beveling is the last part of the lens-making process and creates an edge of the lens to fit snugly into the frame. Most people want their lenses to be as thin as possible. However, there has to be some thickness to the lens in order to maintain the facet, not be too sharp, and avoid easy flaking off of the lens, says Ron Schlotzhauer of Essilor Laboratories of America in the July 2006 issue of Eyecare Business magazine.
Lens Insertion
After a lens blank is surfaced, polished, finished and beveled, the prescription is verified on an optical instrument called a lensometer. This machine checks the lens against the doctor's prescription and measurements and must be used precisely, according to The Eye Care Teachers of America. Once everything in the lenses is determined to be made correctly, the lenses are inserted in the frame and the fit of the lenses is checked for correct alignment before being sent to the doctor's office or optical retail shop to be dispensed to the patient.
Member Comments