contact lens materials
What's New in Silicone Hydrogel Contact Lenses?
BY NEIL A. PENCE, OD, FAAO
There have been many changes in the silicone hydrogel lens category this past year. Here we'll review lens introductions, parameter expansions, new approved indications and name changes.
Late 2007 Approvals
In October 2007, Vistakon added an 8.8mm base curve for its Acuvue Oasys spherical lens. The 8.4mm base curve is still the likely best fit for the majority of eyes. In instances when the 8.4mm lens is too steep, the 8.8mm lens allows a flatter option. This is more likely needed in smaller eyes, and possibly in some very flat corneas.
Also last fall the Oasys lens was approved for therapeutic use, allowing production of plano powered lenses (in 8.4mm base curve only). You can use plano and powered lenses as bandage lenses for acute and chronic corneal disorders. Oasys lenses are approved for up to six nights of continuous wear.
Early 2008 Additions
In April, CooperVision introduced Avaira, a 46-percent water content silicone hydrogel lens material (enfilcon A) with aspheric optics. It's approved for daily wear and has a Dk of 100 and Dk/t of 125 at –3.00D. Avaira also has a 25 percent to 30 percent lower modulus than CooperVision's Biofinity silicone hydrogel lens. The recommended replacement schedule is two weeks.
For comparison's sake, CooperVision's monthly replacement Biofinity lens has a Dk of 128 and water content of 48 percent.
Avaira comes in an 8.5mm base curve, 14.2mm diameter and was introduced with a –0.25D to –6.00D power range. The first parameter expansion expected is higher minus powers.
CooperVision emphasizes the wettable surface and a relatively low modulus for a comfortable lens with very good oxygen transmission for daily wear.
CIBA Vision introduced Air Optix for Astigmatism this spring. The lotrafilcon B material is the same as CIBA's O2Optix sphere product, with a water content of 33 percent. The Dk is 110 with a Dk/t of 108 for a –3.00 –1.25 ×180 powered lens. It's approved for six nights of extended wear.
Lens positioning is achieved by having the thickest parts of the lens at 4 o'clock and 8 o'clock. Orientation scribe marks are at 3 o'clock, 6 o'clock and 9 o'clock. The 6 o'clock line is wider.
The fitting guide lists the recommended replacement as "up to four weeks," but CIBA markets it as a monthly lens.
Initially, sphere powers of plano to –6.00D and cylinder powers of –0.75D and –1.25D were available in 10-degree steps around the clock. Higher cylinder powers are expected next (–1.75D and –2.25D), with higher minus sphere powers following.
Vistakon introduced the Acuvue Oasys for Astigmatism lens last month. The lens incorporates the Acuvue Advance for Astigmatism design but is produced in senofilcon A, Vistakon's spherical Acuvue Oasys with Hydraclear Plus material. The lens is approved for daily wear and up to six nights extended wear. It's recommended for two-week replacement.
Acuvue Oasys for Astigmatism lens parameters include 8.6mm base curve and 14.5mm diameter. The lens is also available in several ranges of sphere and cylinder power. For the complete range, see the Product Spectrum from the June issue of Contact Lens Spectrum.
A Growing Trend
This year has seen the silicone hydrogel segment grow through product introductions as well as new approvals. Utilizing these lenses could help our patients and our practices as well. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #152.
Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana.