Contact Lens Design & Materials
Material for SiHy Daily Disposable Makes U.S. Debut
BY NEIL PENCE, OD, FAAO
Since 2010, Vistakon has sold its 1-Day Acuvue TruEye silicone hydrogel daily disposable lens in two different material versions: narafilcon B in the United States and some Caribbean countries, and narafilcon A in all other markets worldwide. This spring, Vistakon began introducing the narafilcon A material in the United States. After a gradual conversion process in the United States, all TruEye lenses worldwide will be manufactured in the same narafilcon A material.
1-Day Acuvue TruEye was the first silicone hydrogel daily disposable contact lens, a development that allowed the benefits associated with higher oxygen transmission to be available to patients who preferred the convenience and comfort of a single-use lens. First introduced in 2008 in a few markets outside of the United States in the narafilcon A material, the lens has been available in the United States since 2010 in the narafilcon B iteration.
The two versions are very similar. Both have a 14.2mm diameter and power range of −12.00D to +6.00D, and they share the same center thickness and overall lens design. Both feature Vistakon’s Hydraclear 1 Technology, and both exhibit Class 1 UV blocking properties. Each has the same visibility tint and inversion indicator as well.
While very similar lenses, there are some notable differences between the materials. The narafilcon A lens has a higher oxygen transmission, with a Dk/t of 118 compared to 65 for the narafilcon B lens. This higher Dk/t is achieved through a slightly higher silicone content, and thus a slightly different water content (46 percent water for narafilcon A compared to 48 percent for narafilcon B). This small difference in water content has a very minimal effect on the lens modulus, resulting in nearly identical lens handling characteristics.
Another significant difference between the two versions is a second base curve available in the narafilcon A lens. Whereas 1-Day Acuvue TruEye had been available in only one base curve (8.5mm) in the United States, with the conversion it will now be available in base curves of 8.5mm and 9.0mm. This should result in more successful fits on flatter or smaller eyes. Past investigations with Acuvue Oasys (Vistakon) lenses indicated that the flatter base curves allowed more optimal fits on Asian eyes in particular (Chin, 2007), which will likely be true with the TruEye lens as well.
Also corresponding with the conversion in the United States, Acuvue TruEye in narafilcon A will be sold only in 90-pack units. This has always been the most economical way for daily disposable patients to purchase their lenses, and the vast majority of daily disposable contact lens sales are currently for 90-packs.
A Win-Win Situation
Having only one version of a particular product would seem ideal for any company. The choice of the narafilcon A material as that exclusive product has the benefit of offering higher oxygen transmission. U.S. practitioners also now have the added benefit of the second base curve, which should improve fitting success for more patients with this lens. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #211.
Dr. Pence serves as associate dean, Clinical and Patient Services, Indiana University School of Optometry in Bloomington, Ind. He is a consultant or advisor to B+L, Alcon, and Vistakon and has received research funding from AMO. You can reach him at email@example.com.