When a patient orders a pair of glasses they first choose a set of frames that suits them. The patient mush have a prescription must be written by an optometrist which states the needed lens power and pupil distance (PD). Lenses in the needed power are either ordered or taken from stock. These lenses come from the factory as uncut round blanks approximately four inches across. Edging is the process of cutting these optical lens blanks to fit frames, producing a pair of glasses.
There are four pieces of equipment used in the lens edging process. A lensometer is used to check the power in the lens. The tracer is used to determine the dimensions and shape of the frame. The blocker is used to prepare the lens for handling by the edger. The edger cuts the lens to the dimensions specified by the tracer.
Lensometer (Source: Topcon)
Tracer (Source: National Optronics)
Edger (Source: National Optronics)
Step 1 Checking the Lens
After receiving the lens blanks the lab technician first checks them visually for any scratches or imperfections that would be cause for rejection. Next using the lensometer the power of the lens is verified. The lens is rotated to the correct axis (lenses with astigmatism or bifocal correction only) and the optical center (point where the prescription is strongest in the lens) and horizontal axis are marked.
Step 2 Tracing the Frame or Pattern
After lens checking the technician must trace the frame. Tracing determines the needed dimensions of the finished lens. There are two methods of doing this, tracing the frame and tracing the lens. The technician determines which method will work best with a particular frame based on experience and the lab's equipment. In frame tracing the demo lenses or the patients old lenses are removed from the frame and the frame is placed face down in the tracer and held in place with specialized clips. In...