The most cost-efficient and popular method used to manufacture soft contact lenses in bulk quantities is injection moulding. This method is widely used for plastic-based products such as toys. In the production of contact lenses, the lens material is heated to the point of melting. The liquid lens material is then injected into a pre-cut mould. The material solidifies to the shape of the mould once the lens material dries. The lens will be polished, then inspected to check its standard of quality. This particular process lacks the precision required to make hard and gas permeable lenses, hence, it’s only used for soft contact lenses.
Lathe cutting is used to manufacture both hard and soft lenses. It is however, the only way to manufacture rigid gas permeable lenses. Lens cutting uses a technique that puts the lens material on a rotating mount (similar to a miniature potter’s wheel), whilst a machine severs and sculpts away excess lens material to shape a perfectly cut lens. Although this process maintains a greater level of symmetry and lens accuracy, it requires a more complex degree of technology, time and resources in comparison to injection moulding. It does, however, mean that it is ideal for more complicated lens shapes and RGP contact lenses.
The finishing process
The final stage once a contact lens has been cut is quality control and packaging. As contact lenses are considered medical devices, this is significantly important part of the contact lens manufacturing process for the safety of wearers.
During the quality control inspection of contact lenses, the lenses are placed under instence magnification to check for irregularities. Shadow graphing is used to measure the curvature and diameter of the lens. The shadow of the lens is shown on a screen and any faults in the lens shape appear in the shadow.
Packaging contact lenses after they are made
After quality control and the contact lenses have been inspected, they are ready for packaging. Lenses are generally either packaged in a glass vial, or plastic and foil vacuumed blister pack. The vial or blister will be filled with saline solution, a similar consistency to human tears. The hydrophilic material of the contact lens soaks up the saline solution. As the lens in now packaged and sterile, it is now ready for wear.