Silicone hydrogel contacts for up to 30 consecutive days
Conventional hydrogel soft contact lenses can transmit only a limited amount of oxygen to the eyes so that their extended wearing period is also limited to only seven days. The invention of silicone hydrogel contacts changes this situation forever. Its material silicone lets six to seven times more oxygen to reach the eyes and the continuous wearing period has been extended into 30 days. These super-permeable contact lenses have a share of 60% in the soft contacts market.
The design philosophy of silicone hydrogel contacts
Silicone has features that are different from traditional hydrogel polymers, which make use of their water for oxygen carrying and transmission. In contrast, silicone uses both its water and polymer content for oxygen transmission. The latter way definitely is more effective. In fact, water can contain only a small amount of oxygen. Silicone hydrogel contacts have less water and reduce the possibility of dehydration so that long term comfort can be ensured.
Clinical and experimental demonstrations
Silicone hydrogel contact lenses had undergone many tests and clinical experiments before they got the FDA approval. CIBA Vision has conducted an experiment involving 6000 individuals for continuous 30 days wearing of silicone hydrogel contact lenses. The result showed that both microbial Keratitis incidence and its vision acuity reduction rate were considerably lower than 30-day wear lenses in the 1980s: less than 0.18 and 0.04 respectively. In 2005, the University of Manchester published a study result that silicone hydrogel contact lenses were five times less likely to cause Keratitis than traditional hydrogel lenses. All these researches are demonstrations that silicone hydrogel contact lenses are a safer option than traditional lenses.
Silicone contacts in different removal schedules
By providing the same extended vision effect, silicone hydrogel lenses benefit people who need a LASIK but can not afford the high expense or its risk. Actually, silicone hydrogel lenses are approved for different periods of consecutive wearing, not all in 30 days. Only CIBA Vision’s Night & Day and Bausch & Lomb’s PureVision are approved for 30 days, but Acuvue and CooperVision’s Avaira are only for daily wear. There are still some other brands of silicone hydrogel lenses for six-day wearing. Most silicone hydrogel lenses have a replacement schedule between 14 days and 30 days.
30-day silicone hydrogel contacts are limited
Silicone hydrogel lenses are still provided by only a small number of brands and come in fewer lens designs, diameters and curvatures. Toric, bifocal, and custom versions of silicone hydrogel lenses are rarely seen. The above British study also reported that silicone hydrogel contacts had no difference in infection prevention during daytime wearing, but they provide more comfort. So, silicone hydrogel contacts are the preferred option for people who like sleep with the lenses.
Take personal eye condition into account
Individuals always have different eye conditions and eye problem histories. As a result, people should choose different replacement schedules and removal schedules, such as daily wear, common overnight wear and 30-day wear, depending on personal visual condition. You must get a prior recommendation and evaluation from your doctor before choosing 30-day silicone hydrogel contacts.
The reason is that not all people are good candidates for these 30-day contact lenses. In fact, most manufacturers of 30-day contacts preclude certain groups of people for their visual benefit. For instance, people suffering from severe dry eye are not target users of 30-day extended wear contact lenses. Moreover, folks with a history of eye infection are more likely to develop a similar condition if they use extended silicone hydrogel contact lenses.