A contact lens is a lightweight corrective, cosmetic or therapeutic device that is usually placed directly on the cornea of the eye. Contact lenses have many benefits for the wearer, including appearance and practicality. Many people choose to wear contact lenses instead of glasses because they don’t evaporate, they provide a wider field of vision, and are better suited for some physical activities.
Contact lenses vary by material of construction, wear time, replacement schedule and design. In the United States, contact lenses are considered medical devices and require a prescription from a qualified eye care practitioner.
The first contact lens design
Although we think of contact lenses as a modern invention, the concept was first proposed by Leonardo da Vinci. Five hundred years ago, he drew diagrams showing how the refractive power of the eye changes with direct contact with water. Years later, the inventor came up with the idea of putting glass on our eyes to change the way our eyes focus. If they had the materials and manufacturing methods that we have today, their ideas might have developed even further. About 120 years ago, scientists in Germany made the first contact lenses out of glass. They are called scleral lenses because they just sit not on the cornea, the clear dome-like structure at the front of the eye, but on the entire white part of the eye (the sclera).
Around 1940, the first plastic lenses located only on the cornea were developed. This plastic is made of PMMA (polymethyl methacrylate). Because the lens is small, it looks more comfortable. This lens also does not allow oxygen to pass through, and in the 1970s rigid breathable lenses were designed to solve this problem. This mirrors the design of PMMA lenses, but is healthier as it allows more tear flow and oxygen transmission.
Soft Contact Lenses
Also in the 1970s, developers were experimenting with a soft plastic material called HEMA (hydroxyethyl methacrylate). The material absorbs moisture and is flexible so it can be placed over the cornea. Because the plastic conforms to the shape of the eye and is very soft, HEMA lenses provide instant comfort. These lenses are usually designed to last about a year in a pair. As a result, the contact lens industry has developed rapidly.
Disposable Contact Lenses
In the late 1980s and early 1990s, soft disposable lenses entered the market, making contact lenses more affordable and convenient. These lenses are designed to be worn for up to two weeks, one month or one quarter, depending on the type of lens design. Soon after, daily throw lenses came out. Daily disposable lenses are only worn for one day and then thrown away.
In recent years, the focus has turned to silicon-based plastics, which allow more oxygen to flow through the plastic to the cornea. Additionally, manufacturers are continuing their efforts to create a plastic that is more “wettable” and won’t dry out after hours of wear.
Interestingly, scleral lenses are becoming more and more popular. Because today’s manufacturing methods are aided by computer design, scleral lenses can be designed to be very comfortable. Scleral lenses are primarily used in people with severe dry eye, massive astigmatism, and in people with corneal deformities and degeneration.