Silicone Lenses

Silicone Hydrogel Contact Lenses

A new generation of "super-permeable" contact lenses can transmit unprecedented amounts of oxygen to your cornea and, in some cases, enable 30 consecutive days of wear without removal. Silicone hydrogel contact lenses represent a breakthrough over traditional hydrogel soft contact lenses, because silicone allows much more oxygen (essential for a healthy cornea) to pass through the lens. In fact, one recent study shows silicone hydrogel lenses deliver three times the oxygen to the cornea, compared with the leading hydrogel soft contact lens brand.Other data show silicone hydrogel lenses allow up to 5 times more oxygen through the lens than traditional soft lenses (source: CIBA Vision).

Silicone hydrogel contact lenses with high oxygen Dk values, have caught on with both wearers and eye care practitioners. In 2009, silicone hydrogel contacts accounted for approximately 60 percent of new contact lens fittings and lens refittings, compared with 54 percent in 2008, according to equity research firm Robert W. Baird & Co.

How Silicone Hydrogel Lenses Work

Traditional soft contact lenses are made from hydrogel polymers (soft, water-containing plastics). The plastic itself is not oxygen permeable, so the water content performs the job of carrying oxygen through the lens to the eye. But water can carry only so much oxygen — and the more water a lens contains, the greater its tendency to dehydrate after long periods of wear. Silicone is oxygen permeable. So silicone hydrogel lenses use both their water and polymer content to transmit oxygen to the eye.
The benefits to wearers include comfort and convenience:
• Silicone hydrogel contact lenses contain less water than traditional hydrogel lenses. As a result, they aren't as prone to dehydration while you're wearing them. For some people who wear their lenses for long days, this can mean better end-of-day comfort.
• Silicone hydrogels also have made 30-day contact lens wear — sometimes called "continuous wear" — available once again.

30-Day Contact Lens Wear

The initial heyday of 30-day wear was in the 1980s, but that ended due to health and safety concerns.
Today's new silicone hydrogel contact lenses provide much more oxygen to the eye than most conventional soft contact lenses, making 30-day extended wear a safer option than before. As well, the lenses are discarded and replaced monthly, preventing long-term buildup of deposits on the lens surface. The safety of 30-day silicone hydrogel lens wear is illustrated by a clinical study conducted by lens manufacturer CIBA Vision. As part of its approval of Night & Day contact lenses for 30-day wear, the FDA required CIBA Vision to follow the experiences of 6,000 people who were prescribed Night & Day for up to 30 nights of consecutive wear. After one year, the incidence of microbial keratitis (an infection that can result in vision loss) was less than 0.18 percent, and the rate of microbial keratitis resulting in reduction of visual acuity was less than 0.04 percent. These rates are higher than for daily wear, but are still considered reasonable by many as a tradeout for the benefits of continuous wear.

In addition, a British study conducted at the University of Manchester and published in 2005 found that people who slept in traditional hydrogel lenses were five times more likely to develop keratitis than those sleeping in silicone hydrogel lenses.