Contact lenses make life easier for millions of people every day. Prior to the invention of contacts, those with vision problems were required to either wear eyeglasses or suffer with not being able to see very well. While contacts are a modern invention that have changed the way many view the world, most wearers probably do not think about where their lenses come from.
There are 2 main types of contacts that eye doctors prescribe. These include soft contacts, which are generally made to be disposable, and hard contacts, which are meant for long-term use. Each of these are created using different processes and require different materials for manufacturing.
Soft contacts are mass produced using plastic polymers called hydrogels. These materials become soft and gel-like when they absorb water, and require constant lubrication to remain pliable. There are 2 different processes that can be used to produce soft lenses. These are injection molding and lathe cutting.
Injection molding is the most cost-efficient and popular way to produce contacts because it allows for faster production. This task is performed by heating the lens material to its melting point and then injecting it into a mold. It is allowed to dry, where it will take the shape of the mold, which is the precise shape of the needed lens. Once removed, extra material is trimmed, the lens is polished and then it is inspected before being packaged for retail use.
Lathe cutting involves spinning the lens material on a rotating mount while machine-operated cutting instruments precisely sculpt away the excess material. This results in a precision-cut lens that can be easily mass-produced. After being cut, the lenses are polished and checked for quality before being sent off for packaging. Lathe cutting requires a larger amount of resources and time than injection molding, but it also produces a more precise and accurate product.
Mostly all soft contacts are produced using a material called hydrogel, which is a polymer that absorbs water and transmits oxygen through the lens to the eye. Recent scientific discoveries have led to the creation of silicone hydrogel lenses, which boast greater oxygen permeability while remaining thin enough to be comfortable on the eye.
Hard contacts, also known as rigid gas permeable lenses, are custom made to the specifications of each prescription, as they need to fit the size and shape of the eye perfectly in order to be comfortable. All hard contacts are manufactured using a computerized lathe cutting process, similar to that used for soft contacts, because it is the only way to be precise enough to ensure a perfect lens. Most of the time, these lenses are shipped to the eye doctor while they are still hard, and the doctor will soak them in a special solution before dispensing them. This solution helps condition the lenses for greater comfort.
Hard contact lenses are produced using hard polymers, or plastics, which are porous enough to allow oxygen through to the eye. In order for the lenses to be able to achieve maximum breathability, scientists have added fluorine to the lens material, which allows for greater oxygen permeability on a long-term basis.