subject: How are lenses made? [print this page] Glass was traditionally used for making lenses, but today many are plastic as it is easier to shape the plastic lenses ready for the frames, as well as plastic being stronger, so it can be ground thinner than glass.
When your lenses are being made, the first step in the process is the selection of a blank lens. Usually, a lens of strength +6 is chosen, and the lens side that is not being ground is covered with protective tape. The lens is placed on a chuck receiver (a block) and is passed into a generator- a specialised piece of machinery that grinds a curve into the upward facing side of the lens. To get a +2 prescription from a +6 lens, a 4 curve is ground into the lens. If a 2 prescription is required, a 8 curve is ground into the +6 lens.
After the lens has been ground to the required prescription, it is removed from the generator and placed in a cylinder machine that sands the lens to remove marks left by the generator. This is followed by a polishing stage, where the lens is polished to remove all scratches from the surface that has been worked on.
In order for the lens to be shaped to fit your chosen frames, the lens is placed on a small chuck receiver over the centre of the new shape of lens. The lens and chuck receiver are placed in an edger, which uses ceramic or diamond wheel to grind away the edges of the lens until the correct shape is achieved. The edger is either manually controlled, or (more commonly) receives information about lens dimensions from a computer and automatically grinds the lens to size.
The new lenses are fitted to the frames selected by you, and are returned from the lab where this process takes place, to the opticians for you to collect.
