Silicone Hydrogel Contact Lenses: A Look Ahead?

Silicone Hydrogel Contact Lenses: A Look Ahead?

More than 20 years ago, someone came up with the idea of making lenses out of silicone hydrogel. It was evident what the possible benefits were, but the technological barrier was as hard as mixing oil and water to make a clear product. Research organisations have put a lot of time and money into making the high-performance soft lenses we have today. They have done this because they believe that this content is the best way to go and the best standard for the future.

At the time this was written, four companies in the US made silicone hydrogel lenses: CIBA Vision made "Night & Day" and "O2OPTIX," Bausch & Lomb made "Pure Vision," and J&J Vision Care made "Acuvue OASYS" and "Advance."

OXYGEN TRANSPORT

What's so great about silicone hydrogel as a lens material? The key benefit of this material is that it can carry oxygen to the eye and keep it healthy. The "Dk" index is used to measure how well modern contact lenses let oxygen through. And for the best oxygen transport, this needs to be as high as it can be.

The Dk of traditional hydrogel lenses that don't employ silicone is directly proportional to how much water the material can store. This is because oxygen dissolves in the water part of the material and then spreads through the lens. The Dk actually goes up in a logarithmic way as the water content goes up. Water has a Dk of just 80, which means that conventional materials can't have a Dk higher than that. The original soft contact lens material, polyHEMA, had a Dk of only about 10 (with a water content of about 38%).

In silicone hydrogels, though, the relationship between Dk and water content is the other way around. In this case, more water means a lower Dk. With these lenses, Dk goes up a lot as the silicone content of the lens goes up, not the water content. The Dk values of silicone hydrogel contact lenses are substantially greater than those of earlier soft lens materials.

SLEEPING WITH CONTACT LENSES

CIBA Vision's market data shows that 84% of people who wear soft contact lenses sometimes sleep with them in, and one-third say they do this all the time. Some people who wear one- to two-week disposable lenses that don't let oxygen through sleep in their lenses at night. Also, 72% of people who wear soft contact lenses stated they would rather be able to wear their lenses overnight if it was safe.

So, it's clear that there is a very large demand for lenses that can do what silicone hydrogels can do. Almost three-quarters of people who use soft lenses want to be able to sleep in them.

How to Handle Lenses

Silicone hydrogel lenses are more stiffer than regular lenses because they include silicone. This added rigidity does have certain benefits, making the lenses more easier to handle and making them the best alternative for people who don't have a very delicate touch. But there is a drawback to this: the stiffness makes the lenses less likely to fit the contour of the eye easily, which could make some people less comfortable.

FEWER DEPOSITIONS

In the past, contact lenses have had problems with proteins and lipids building up on them. The number of deposits is mostly determined by how long the lens is worn, what it's made of, and how many tears each person has. With regular lenses, changing them often helps keep dangerous deposits from building up.

Silicone hydrogel contact lenses have been shown to be very helpful in lowering the buildup of protein and lysozyme. In fact, difficulties with protein deposition are nearly a thing of the past now that the right replacement schedule and care system are in place.

DRY EYES

People who wear typical soft contact lenses often have a problem at the end of the day where their eyes feel uncomfortable and "gritty." A study found that after one week of wearing silicone hydrogel lenses, the number of normal soft lens wearers who had a lot of dryness at the end of the day dropped considerably to only 13% of the sample.

Advantages for your way of life

There are also certain benefits to silicone hydrogel contact lenses that regular lenses don't have. People who work in certain fields, like medicine, law enforcement, the military, and firefighting, may find continuous use contact lenses especially useful because they often have long, unpredictable hours.

Also, more and more people who wear contact lenses may now live active lives outside, doing things like camping and hiking where it can be hard to clean and care for the lenses in a way that is safe.

THE FUTURE OF CONTACT LENSES

There is a lot of evidence to suggest that silicone hydrogel lenses will eventually replace other types of contact lenses as the most popular choice for both daily and overnight wear for most people who wear contact lenses. This is because they have many advantages over regular soft lenses. Silicone hydrogel lenses work significantly better physically, are easier to handle, and are more comfortable. They may be seen as the best lens for everyday use that is available right now, and they are likely to become the new standard.

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