Friday, November 30, 2007

Silicone Hydrogel Contact Lenses

Silicone Hydrogel lenses are the latest development in soft contact lens materials. They are healthier than conventional soft lenses because they allow up to 6 times more oxygen to pass through them and increased oxygen transmission results in better overall eye health. Advantages of silicone hydrogel lenses over conventional soft lenses include: more resistance to protein deposits, less drying of the lenses, lower risk of eye infection, easier handling due to increased rigidity of material, and much lower incidence of complications with extended wear use (overnight wear).
The convenience of 30 days continuous wear (PureVision and Focus Night & Day), as well as the lowered incidence of eye health complications are quickly making silicone hydrogels the most popular lens of choice for both eye care practitioners as well as patients. Most eye doctors believe that within the next 5 years, more patients will be wearing silicone hydrogel lenses than any other lens material.

The current brands of spherical silicone hydrogel lenses available, in order of highest oxygen transmissibility to lowest, are:
  • Ciba Focus Night & Day which is approved for 30 day continuous wear
  • Vistakon’s Acuvue Oasys which is approved for 2 week daily wear use or 6 night extended wear and is designed to be more wettable than the others and is therefore beneficial for people who have dry eyes
  • Ciba’s O2 Optix which is approved for 6 days continuous wear or 2 weeks daily wear
  • Bausch & Lomb’s PureVision which is approved for 30 days continuous wear
  • Vistakon Acuvue Advance which is a 2 week disposable lens and has not yet been approved for extended wear.

There are also currently two toric (astigmatism correcting) silicone hydrogel lenses on the market:

Studies have indicated that some lens care cleaning systems are compatible with silicone hydrogels, while others may cause adverse reactions due to toxicity. Aquify, Optifree Express, and ClearCare multipurpose solutions have all been FDA approved to be used with silicone hydrogels.
AOSept has proven to be an acceptable hydrogen peroxide based system to use with these lenses. In some studies, Renu Multiplus has been shown to cause an adverse corneal reaction when used with some silicone hydrogel lenses (source Contact Lens Spectrum, August 2005). Additionally, UltraCare and SoloCare are not recommended for use with silicone hydrogel lenses.

Most people would benefit from wearing silicone hydrogel lenses as compared to conventional soft lenses due to the health advantages, however, these lenses are especially useful in the following types of patients: people with high prescriptions; those whose eyes show signs that they require more oxygen; wearers who experience end of day discomfort, dryness, or redness with their conventional soft lenses; people who wear their lenses for more than 12 to 14 hours a day (including overnight wear); and kids and teenagers who tend to routinely over wear their lenses. Additionally, since the Focus Night & Day as well as the PureVision lenses are approved for 30 days of continuous wear, they can be considered as a useful alternative for people contemplating refractive surgery.

Silicone hydrogels may not be the lens of choice for all patients. These lenses are generally more expensive than non-silicone lenses so a more price conscious consumer may not prefer this option. Also, in some wearers, the silicone material tends to attract more lipid deposits, which may cause blurred vision and discomfort. There are some cases where a patient is not able to adapt well to the more rigid silicone material, which may result in some minor defects to the corneal integrity.
These complications are rare and generally the health advantages and increased comfort that most wearers experience far outweigh the incidences of adverse reactions in those who do not adapt well to the material.

(c) 2006 AC Lens, Reproduction Prohibited without Express Permission

Focus Night & Day were the subject of a three year study by Ciba Vision. The company reported that the performance of this silicone hydrogel (SiHy) contact lens indicated that wearers enjoyed improved corneal health and reduced frequency and symptoms of contact lens related eye health symptoms.
In particular, the study of 317 patients showed that Focus Night & Day wearers had less problems with red eye, reduced dryness (22%) and neo-vascularization (the development of new blood vessels in the cornea) was reduced by 13%. During the first 8 months of 2005, Silicone Hydrogels represented 24% of all soft contact lens sales – more than double the figure for the same period of 2004. Ciba lenses represented almost 50% of silicone hydrogel sales during this time.

Bausch & Lomb (manufacturer of Purevision, Purevision Toric and Purevision Multifocal contact lenses) reported that 40% of new contact lens fits are now silicone hydrogel contacts. They claim that 94% of wearers of their sector leading Soflens 66 Toric contacts can be migrated to the Purevision Toric lens without a script change.

Vistakon, manufacturer of the Ultra-Comfort series of contact lenses which comprises the Acuvue Advance, Acuvue Advance for Astigmatism and the Acuvue Oasys says their silicone hydrogels are all addressing the
issue of end-of-day comfort for contact lens wearers. Prescription parameter ranges are being expanded for each of these lenses (most recently, plus powers for Oasys were made available). Acuvue Oasys
was also recently given FDA approval for up to 7 days of continuous wear. Vistakon claims to have the number one silicone hydrogel with their Acuvue Advance and the number one new-wearer toric in the Advance
for Astigmatism.
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