The Science Behind: Contact Lenses
Through these tiny miracles, people are able to see clearly without having to worry about where they put their glasses. Contact lenses are commonly used because of their oxygen permeable material and their different types: soft lenses, rigid gas permeable lenses, and hybrid lenses. Each is made for a different wear length, therefore resulting in slightly different processes of making them. The same applies to the material from which contacts are made; they are made of hydrogels or water-loving plastic polymers, resulting in some lenses holding as much as 70% water. Soft contact lenses are called “soft” or “hydrogels” due to their water-loving property.
There are two ways to make soft contact lenses: lathe cutting or injection molding. Lathe cutting is performed when small, hard disks of the polymer are spun at 6,000 revolutions per minute and shaped using a computer cutting tool. Injection molding is when the polymer is heated until it becomes liquid and then it is cooled in precise, pressurized molds. Both processes require the lenses to be polished and hydrated until their quality is deemed fitting.
Although rigid gas permeable contact lenses are made of water-loving plastic polymers, they are coated with silicon and fluorine which makes the lenses more durable than soft contact lenses. These are made for longer wear and are made using the precise lathe cutting for the soft lenses mentioned above. The difference in the process occurs with the hydrating; they are shipped dry and hydrated in a solution at a doctor’s office instead of being hydrated and then tested for quality.
Hybrid contact lenses are a combination of the two types mentioned as suggested by their name. Hybrid contact lenses have a central zone made of rigid gas permeable lens material and outside or border made of soft contact lens material. These are also made using the lathe-cutting technique. Each of the two sections of the hybrid lens is made separately. The soft contact lens section is hydrated only after the two sections are combined, as is the rigid gas permeable section. Thanks to this process, many are able to see with tiny pieces of plastic which can be on the eye from a day to a month straight!