In this blog post, we’ll explore how contact lens materials have evolved and examine the advantages and limitations of the materials used in each era.
The Beginnings of Contact Lenses and Early Materials
Carrying something that isn’t part of your own body can be quite uncomfortable. As medical technology has advanced, people have replaced uncomfortable parts of their bodies with artificial materials; some even insert silicone into their faces or get body piercings for aesthetic reasons.
Among the objects we carry inside our bodies that aren’t part of us, contact lenses are by far the most widely used. The cornea is very thin and sensitive, so even a tiny speck of dust can cause significant irritation. Wearing a contact lens on the cornea as if it were a natural part of the body is not a natural state, so there is a possibility of side effects. Nevertheless, the widespread adoption of contact lenses that cover the entire cornea indicates that the materials used provide sufficient comfort for many people to wear them, and that advances in medicine and materials engineering have succeeded in significantly reducing side effects. So, how have the side effects of contact lenses been reduced? Let’s examine this by focusing on the evolution of contact lens materials.
In 1887, the “glass scleral lens” was invented by German ophthalmologist Adolf Eugen Fick. This was the first contact lens, created by filling the space between the front and back surfaces of a glass lens with a liquid that had a refractive power nearly identical to that of the cornea. Unlike the lenses widely used today, the lens’s support structure covered the sclera—the white part of the eye—and did not come into direct contact with the cornea. This design avoided contact with the cornea, the most sensitive part of the eye.
The Emergence of Corneal Lenses and RGP Lenses
With the development of the plastics industry in the 1930s, plastic scleral lenses were produced, with the corneal portion made of glass and the scleral portion made of plastic. Around the same time, scleral lenses made from the synthetic resin PMMA (polymethyl methacrylate) also appeared. PMMA, commonly known as acrylic resin, is a thermoplastic material with exceptional transparency. With the introduction of PMMA, corneal lenses—which eliminated the scleral portion—gradually became the standard. This signified that contact lenses had evolved from a structure supported on the sclera to one that made direct contact with the highly sensitive cornea.
Although corneal lenses continued to evolve in various forms through the 1970s, PMMA had limitations due to its rigidity and its inability to allow oxygen and moisture to pass through.
Because PMMA has very low oxygen permeability, wearing these lenses could lead to various side effects caused by corneal hypoxia. To address these issues, “rigid gas-permeable lenses (RGP lenses)” were developed. RGP lenses use materials that allow oxygen to pass through easily, such as silicone, silicone acrylate, and fluorosilicone acrylate.
The oxygen permeability of contact lenses is generally expressed as the DK value (Dk). RGP lenses have significantly higher oxygen permeability than PMMA lenses, greatly increasing the amount of oxygen delivered to the cornea, which played a crucial role in maintaining corneal health.
The development of highly oxygen-permeable lenses is significant not only because it improved comfort but also because it marked the beginning of a focus on eye health. However, while RGP lenses could supply sufficient oxygen to the cornea, the discomfort associated with wearing them—due to their rigid material—remained unresolved.
Advances in Soft Contact Lenses and Silicone Hydrogel
Soft contact lenses emerged as new materials were introduced to compensate for the rigidity of PMMA. The most common materials are hydrogel and silicone. Hydrogel has the advantage of high water content and excellent comfort. However, they maintain their soft and elastic properties only when hydrated; once they dry out, the lenses become hard. They also had the limitation of relatively low oxygen permeability.
Silicone, on the other hand, has very high oxygen permeability but low hydrophilicity, so it does not absorb moisture well. Silicone hydrogel combines the advantages of these two materials. Silicone hydrogel combines high oxygen permeability with excellent hydrophilicity, significantly overcoming the limitations of traditional soft lenses, and has established itself as one of the most widely used contact lens materials today.
As we’ve seen, contact lenses have continuously evolved, starting from fragile glass materials and progressing through plastic, PMMA, RGP materials, and finally to silicone hydrogel. However, the fact that contact lenses are, by their very nature, foreign objects in contact with the human cornea remains unchanged. Even if superior synthetic materials are developed in the future, this fundamental characteristic will persist.
Biologically speaking, natural materials that more closely resemble the human body could serve as ideal contact lens materials. For example, collagen lenses—which utilize collagen, a major component of the human cornea—are being proposed as one possibility. While research is currently underway in the fields of tissue engineering and biomaterials using biocompatible materials such as collagen, manufacturing technology for collagen lenses capable of replacing the actual human cornea or being commercialized like standard contact lenses has not yet been established. Therefore, this technology remains an area requiring continued research.
