Silicone Hydrogel Contact Lenses

Perhaps you've heard about the newest in contact lens materials -- silicone hydrogel. Maybe you've only heard from your eye doctor that there are new, and (arguably) much better contact lenses available. But what does it mean? Maybe you've been told that your new contact lenses provide more oxygen to your eye - but how much? Just how much better are these new contact lenses than your old contacts?

Silicone hydrogel contact lenses include the following:

• Acuvue Advance (also Acuvue Advance for Astigmatism)
• Acuvue Oasys
• O₂ Optix
• Purevision
• Focus Night & Day

Chances are, you've heard about at least one of these - whether it was on TV or in a magazine. Most of the contact lens manufacturers are really pushing silicone hydrogel lenses, and for good reason. These new contact lenses are a much healthier choice for your eyes. However, while all of these contact lenses are made with silicone hydrogel, they are not all created equal. The first three contacts that are listed above (Acuvue Advance, Acuvue Oasys, and O2 Optix) are the newer brands that have been marketed for daily wear only. Purevision and Focus Night & Day have been around for a few years now and are very popular as continuous wear contact lenses. Differences among these contact lenses is most apparent in their oxygen permeability and rigidity.

Silicone Hydrogel and Oxygen Permeability

When an optometrist decides which contact lenses are right for your eyes, he/she looks at the Dk value of different contact lens materials. Each contact lens material has a specific Dk value, which indicates just how permeable that contact lens material is to oxygen. The higher the Dk value, the better it will transmit oxygen from the air to your eye. The hard contact lenses of the 1970s and 1980s (PMMA) had a Dk value of zero, meaning absolutely no oxygen was getting to the eye through the contact lens material. Typical conventional contact lenses (the contact lenses that you were likely wearing 5-10 years ago) generally have a Dk value somewhere between 20-30 or lower. Silicone hydrogel lenses, on the other hand, have much higher Dk values, ranging from 60-140. This improvement in oxygen permeability means that your eyes are exposed to conditions that are as close to natural as currently possible - almost as if you weren't wearing contact lenses at all. This is the ultimate goal in contact lens research, and silicone hydrogel lenses are the nearest that researchers have come to reaching this goal.

Hard Soft Contact Lenses?

Due to the presence of silicone in silicone hydrogel contact lenses, the lenses become much more rigid compared with conventional soft contact lenses. While this difference is hardly noticeable in some people, other contact lens wearers find the rigidity of silicone hydrogels too much to bear and must go back to the older style of contact lenses. When your eye doctor first fits you with new contact lenses, he/she will ensure that you return to the clinic for a follow-up appointment in order to make sure that the silicone hydrogel contacts are suitable for you. Remember that there may be an adaptation period to wearing the contacts.

How Silicone Hydrogel Contact Lenses Will Affect You

One of the most common complaints about contact lenses is the need to remove them before the day end due to symptoms of dryness and discomfort. A recent study has shown that wearing silicone hydrogel lenses (this particular study was performed using Acuvue Oasys lenses) contributes to longer wearing time and reduced symptoms of dryness. Silicone hydrogel lenses are also less likely to accumulate protein deposits.

The Bottom Line - Are Silicone Hydrogels Right For You?

This is a decision that of course can be made by you, and you alone. The optometrists who are up with the times should most certainly offer silicone hydrogels as an alternative to your current contact lenses. As the long-term effects of using contact lenses with no oxygen permeability are becoming more and more evident (I'm talking about you baby boomers who wore the first generation of hard contact lenses!), making sure that your eyes are receiving as much oxygen as possible couldn't be more obvious. You've only got two eyes, and they've got to last you an entire lifetime - be good to them!