|Contact lenses have made life easier for millions of people worldwide ever since they've been able to be mass produced for public use. With such a widespread adoption of contact lenses, many wonder how manufacturers are able to make such a large quantity of precision contact lenses in such an efficient manner.
It's important to remember that there are two primary varieties of contact lenses. The most popular variety of contact lens is the soft contact lens, traditionally made in disposable varieties. The other type of lens is the RGP, or Rigid Gas Permeable lens, which uses a harder material for long-term use.
The Manufacturing Process for Contact Lenses
Injection Molding The most popular and most cost efficient method to manufacture soft contact lenses in large quantities is through the use of injection molding. Injection molding is a very common and popular way to manufacture a wide variety of objects, and is used to create anything from action figures to medical devices such as contact lenses. Injection molding is particularly popoular with plastic-based products.
Injection molding for contact lenses is performed by heating the lens material to the point of melting, then injecting the liquid lens material into a pre-cut mold. Once the lens material dries, it will solidify in the form of the mold, giving precise shape to the lens. After the lens is removed, extra material may be removed, and the lens will be polished prior to being inspected for quality. Injection molding is used only for soft contact lenses, as the process lacks the precision detail required to produce hard gas-permeable contact lenses.
Similar to a potter's wheel on a much smaller scale, lathe cutting puts the lens material on a rotating mount, while machine cutting instruments sculpt away excess lens material to carve a precision-cut lens. The lenses are then polished and checked for quality before being packaged for retail. Lathe cutting requires a higher degree of technology, resources, and time when compared to injection molding, but also gives a higher level of precision in lens accuracy, making the process ideal for more complex lens shapes and RGP contact lenses. Lathe cutting is used for both hard and soft contact lenses, although it is the only way to manufacture Rigid Gas Permeable Contact Lenses.
Materials Used To Make Contact Lenses
Materials Used For Soft Contacts
These days, most soft lenses are made out of a material known as Hydrogel, a water absorbing polymer that uses the water content to transmit oxygen to the eye through the lens.
Hydrogel lenses are usually graded on how much water they hold, with some lenses holding as high as 70% water. While water does increase oxygen permeability, it also increases the size of the lens, which may in turn cause increased discomfort. Less water typically results in a thinner lens.
Silicone Hydrogel are an even newer type of lens material that has been developed for greater oxygen permeability while avoiding added bulk of larger lenses. Adding silicone to the hydrogel lens has shown to increase oxygen permeability by a significant amount, which many major lenses now make use of for added comfort.
Materials Used To Make Hard Contact Lenses
Hard contact lenses are manufactured with hard polymers (plastics) that are naturally porous enough to allow oxygen to reach the eye. The hard plastics give the lens wearer a higher level of optical clarity at the risk of initial discomfort while getting used to the lens. While soft contacts require water to transmit oxygen through the lens, hard lenses don't have this option, so they need to use materials that can naturally transmit oxygen from one side to the other in an incredibly efficient manner.
In order to achieve a high level of oxygen breathability, scientists had to add fluorine to the lens material to achieve the required oxygen permeability that would allow hard lenses to be worn on a long-term basis. Through adding fluorine, rigid lens materials develop microscopic holes and pores which allow oxygen to flow freely through the lens despite the fact that the lens is a solid material.