contact lens materials
Silicone Hydrogels — No Longer for Just a Select Few
BY KATHY DUMBLETON, MSC, MCOPTOM, FAAO, & LYNDON JONES, PHD, FCOPTOM, FAAO
When silicone hydrogel lenses were introduced in certain countries 10 years ago, they were considered a premium product and prescribed predominantly for overnight wear. The clear physiological advantages of these materials resulted in many new silicone hydrogel lenses becoming available. Practitioners started to consider this technology for more of their patients on any wearing schedule. More than 50 percent of fits and refits are now estimated to be with silicone hydrogel materials.
Unfortunately, many patients continue to report discomfort and reduced wearing time with their lenses. It's not surprising that research and development continues to optimize parameters that may lead to increased comfort. Two new silicone hydrogel lenses aim to address this with the addition of wetting agents or increased replacement frequency.
Air Optix Aqua (CIBA Vision) employs a plasma coating and hydrophilic moisture agent said to bind to the lens surface and enhance comfort on application. The lotrafilcon B material has a lower initial contact angle than the original material and reportedly increased deposit resistance.
Avaira (CooperVision) was recently launched in the United States as a two-week replacement, daily wear silicone hydrogel lens. The material (enfilcon A) utilizes technology similar to comfilcon A for the Biofinity lens, reducing the need for any surface treatment or modification to ensure adequate wettability and low modulus. Avaira also features aspheric optics and a UV inhibitor.
Torics and Multifocals
In addition to extended power ranges for spherical silicone hydrogels and the availability of custom silicone hydrogel lenses, over the last year we've seen the introduction of two new silicone hydrogel toric lenses: Air Optix for Astigmatism (CIBA) and Acuvue Oasys for Astigmatism (Vistakon). When combined with other toric silicone hydrogels, it's estimated that 30 percent of toric fits are now with these materials.
Our presbyopic patients are no longer being left behind with several multifocal silicone hydrogel lenses available. The PureVision Multi-Focal (Bausch & Lomb) has been available for some time, and the Air Optix Aqua Multifocal (CIBA) was recently introduced in Europe and will soon be available in North America. Acuvue Oasys for Presbyopia (Johnson & Johnson/Vistakon) is also being gradually introduced around the world. Many consider it time-consuming to fit presbyopic patients with multifocals, but a study conducted at the Centre for Contact Lens Research at the University of Waterloo presented at the 2008 American Academy of Optometry meeting demonstrated that fitting a first-time presbyopic patient with the lotrafilcon B aspheric multifocal lens required the same chair time as fitting a monovision patient.
Compliance and convenience are also major issues for lens wearers. While our European counterparts have embraced the daily disposable modality to meet these issues, North America has been slow to adopt this modality. Perhaps this will change with new daily disposable silicone hydrogel lenses. One is already available in the United Kingdom: the 1-Day Acuvue TruEye (J&J). We reported on this lens in February.
With the plethora of designs available in silicone hydrogel materials, you should consider these lenses for most patients and no longer for just a select few. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #161.
Dr. Dumbleton is a senior clinical scientist at the Centre for Contact Lens Research in Ontario, Canada. Dr. Jones is the associate director of the Centre for Contact Lens Research and a professor at the School of Optometry at the University of Waterloo, Ontario, Canada. He has received research funding from Alcon, AMO, B&L, CIBA Vision, CooperVision, Johnson & Johnson, and Menicon.