Contact Lens Design & Materials
Can I Get That in a Silicone Hydrogel?
BY NEIL PENCE, OD, FAAO
"Lucy" is a 25-year-old who has a spectacle prescription of OD –16.50 –4.75 × 180, OS –14.50 –3.00 × 180. She is wearing a custom hydrogel toric. Needless to say, she prefers her contact lenses over her thick glasses and she sees more than one line better with her contact lenses as well.
There is certainly some concern for this patient regarding the amount of corneal hypoxia the lenses might be inducing. We have become very familiar with the advantages of silicone hydrogel (SiHy) lenses in alleviating the corneal signs of lens-related hypoxia. Higher oxygen transmission is also effective at limiting limbal vascular changes and allowing generally whiter eyes. In the case of this patient, this leads to the obvious question—"Can I get that in a silicone hydrogel?"
Custom SiHy Lens Options
O2Optix Custom The O2Optix Custom from Ciba Vision is very similar in material to Air Optix Aqua (Ciba), with slight alterations to allow better success when lathe cutting. The lens is available in spherical prescriptions only, with a power range of ±20.00D, three diameters, and four or five different base curves depending on the diameter. After evaluating a first diagnostic lens, O2Optix Custom comes in fourpacks to be replaced on a quarterly basis. This lens has been helpful to patients who have very high prescriptions for which a spherical lens is applicable.
Definitive Silicone Hydrogel Material In late August, Contamac received FDA approval for Definitive, a 74-percent water content SiHy material with a Dk of 60 that is capable of being lathed, making it suited for all forms of custom soft lenses. While this oxygen permeability is the lowest of all SiHy materials, it provides roughly three times more oxygen than most hydrogels do.
Custom lenses manufactured by Ultravision in the Definitive material have been available in Europe for several years in a wide variety of designs including spheres, torics, multifocals, and keratoconic lenses. The Ultravision lenses were used in clinical studies to obtain the FDA approval, and those studies were summarized in the September issue in "A New Era of Specialty Soft Contact Lens Fitting" (Koch, 2010).
In the United States, Art Optical, Metro Optics, Unilens, and X-Cel Contacts will be offering custom contact lenses in the Definitive material. Each company is required to receive individual FDA approval for lenses to be manufactured in the Definitive material. It is anticipated that these companies would seek approval to use Definitive in a number of their current designs.
For example, it is reasonable to expect Art Optical to produce its Intelliwave line of spheres, torics, and multifocals in Definitive. Likewise, X-Cel might be expected to use Definitive for its Flexlens and Westcon designs. Metro Optics has the RevitalEyes lens approved for post-refractive surgery, which would be an excellent option to have in a higher-Dk material. Similarly, Unilens is expected to manufacture some of its existing designs in Definitive, offering more choices for custom SiHy contact lenses.
More Choices for More Patients
The new latheable Definitive material will bring higher oxygen transmissibility to many types of custom soft contact lenses. Many specialty lens patients and patients who have high prescriptions, such as "Lucy" above, will benefit from having more higher-Dk lens options. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #180.
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.