Materials of contact lenses

There are three great families:

1- Soft contact lenses: Otto Wichterle, a Czech chemist, invented a hydrophilic gel (hydrogel), which was marketed in the early seventies with great success because it was comfortable at once.

 

The secret is that these contact lenses contain a lot of water (low water content, less than 40%, half, between 40% and 60% and higher, more than 60%).

Water content influences comfort, but also on oxygenation in the eye. The more water, the more oxygen. The problem is that the more water, the weaker the contact lens. So, what manufacturers are doing is to play with the thickness and with different components that place in the matrix of the material.

Another important feature is the surface charge. There are the ionic materials (with negative charge) that attract tear protein deposits, so the non-ionic ones were developed later.

2- Silicone hydrogel contact lenses: they were introduced in 2002. The main difference is that they contain silicone. Silicone allows a very large oxygen flow, but it has the problem that it has a very low wettability and a high lipid adhesion. For this reason, it was sought to combine it with silicone hydrogels. It was a very difficult process (it's like water and oil), but it was achieved and at present they are the best-selling contact lenses. Current brands often carry an ionic surface treatment to improve comfort of use.

3- Gas permeable contact lenses. The first lenses of plastic material were marketed in 1948. They were PMMA (polymethyl methacrylate). It was an excellent material for its optical properties, durability and biocompatibility, but they were not porous. The eyes oxygenated because contact lenses were of a small diameter and moved. In 1979, the first permeable gas rigid lenses were introduced in the United States. They were silicone acrylates. Over the years, they have evolved into fluor-silicone acrylates, which improves moisture, material stability and oxygenation.

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