Contact Lens Design & Materials
The Year in Silicone Hydrogels
By Neil Pence, OD, FAAO
In this month's column, I will review introductions, parameter expansions, and other changes in the past year in the category of silicone hydrogel contact lenses.
Daily Disposable Lens
The most significant news has been the creation of a new segment of silicone hydrogel lenses. 1-Day Acuvue TruEye (Vistakon) became the first silicone hydrogel daily disposable in the United States with its June 2010 release. TruEye was introduced in powers ranging from +0.50D to +6.00D, −0.50D to −6.00D (all in 0.25D steps), and −6.50D to −12.00D (in 0.50D steps). The lens has a 14.2mm diameter, 8.5mm base curve, is visitinted, has the 1-2-3 inversion mark, and is available in 30 and 90 packs. The lens can also claim the highest UV protection of any daily disposable.
TruEye is manufactured in narafilcon B material, which has a Dk/t of 65 and a center thickness of 0.085mm for a −3.00D lens power. This means TruEye transmits roughly three times more oxygen than previously possible in hydrogel daily disposables. While daily lens wear does not demand the same level of higher oxygen that overnight or continuous wear might, this option could clearly benefit some patients. Patients wearing thicker, higherpowered lenses routinely for most or all of their waking hours are at risk for corneal hypoxic complications. When daily disposables were introduced it was easy to make the case for them as the healthiest soft lens option. With the advent of silicone hydrogels and the higher levels of oxygen that they allow, the argument was less clear-cut. With higher-oxygen-transmission daily disposable lenses now available, we may now be able to make the case for this being the healthiest, safest possible way to wear soft lenses.
TruEye employs Hydraclear 1 as an embedded wetting agent that has been shown to keep moisture at the lens surface throughout the day (Sheardown, 2009). It may also be a factor in the excellent initial on-eye comfort that patients and at least one investigation have reported, likening it to the ocular sensation of no lens at all. (Morgan, 2009)
Silicone Hydrogel Multifocals
This past year also saw introductions of two more lenses in the silicone hydrogel multifocal category—Acuvue Oasys for Presbyopia from Vistakon and Air Optix Aqua Multifocal from Ciba Vision. These lenses have provided more options for presbyopic patients while allowing high oxygen transmission and excellent comfort and wetting, helping to grow this lens category. With a rapidly increasing population in need of reading help, multifocal lens use will only increase, and having multiple options is very helpful.
Acuvue Oasys for Presbyopia is a center-distance lens utilizing an aspheric ring zonal design, while the Air Optix Aqua Multifocal is a center-near design. For a more in-depth look at these lenses, see the February 2010 Contact Lens Design and Materials column by Ron Watanabe, OD, FAAO.
Silicone Hydrogel Multifocals
CooperVision has expanded the parameters of its Biofinity Toric lens since its introduction more than a year ago. It is now available in sphere powers from +8.00D to −10.00D (0.50D steps over 6.00D), and −0.75D, −1.25D, −1.75D, and −2.25D cylinder powers in 10-degree steps around the clock.
CooperVision also received FDA approval for Avaira Toric and began a limited release of the lens. Avaira is CooperVision's slightly lower oxygen silicone hydrogel lens (compared to Biofinity), intended for two-week replacement. Avaira Toric was released with sphere powers from plano to −6.00D, and cylinder powers of −0.75D, −1.25D, and −1.75D in 10-degree steps around the clock. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #178.
Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana. He is a consultant or advisor to B&L, Ciba Vision, and Vistakon, and has received research funding from AMO. You can reach him at email@example.com.