contact lens materials
GP Materials Offer New Options and Convenience to Patients
BY NEIL PENCE, OD, FAAO
This month we look at what's new regarding GP lens materials. While there is generally less activity compared to soft lenses, significant developments have occurred in GP materials.
New GP Offerings
Bausch & Lomb introduced Boston XO2 more than a year ago. This material allows more oxygen transmission (Dk of 141) than Boston XO, yet machines and wets as well as the lower-Dk material. These features make XO2 a great choice when a little higher oxygen is desired, such as higher prescriptions with thicker profiles, or for patients who may have worn XO in the past.
B&L also announced that Boston ES will become available in a clear version. Only the rare patient wants clear lenses, but some practitioners find it easier to view fluorescein through clear diagnostic lenses. With the advent of clear Boston ES, expect clear options for older Boston materials to be phased out.
Paragon has introduced the SureFit 1-Day GP Fitting and Dispensing System. It is a program to increase first-day fitting success and to reduce chair time. Lenses are ordered empirically based on the design and prescription. A consultant determines the best combination of lenses to cover a number of variables. It results in patient-specific diagnostic sets of two-to-four lenses per eye. The hope is to make GP fitting and dispensing more similar to what we have come to expect from soft lenses — patients walk out with lenses after the fitting visit. Labs are expected to have various spherical and multifocal designs in SureFit.
As discussed by Edward Bennett, OD, MSEd, in last month's GP Insights column, there are new higher-index of refraction GP lens materials that allow for thinner, lighter lenses. This might help with centration and comfort. Higher-index materials might also allow beneficial design changes, such as larger optic zones or larger diameters, without increasing lens thickness or weight. All of the higher-index materials also have lower specific gravities, resulting in lighter-weight lenses.
Another benefit is the enhanced refractive effect that high-index GP materials might have when used in aspheric multifocal designs. With the same amount of asphericity, a higher-index material will produce an increased add effect. One of the limitations of aspheric multifocals is producing higher adds. Combinations of front and back asphericity are often used, but seldom result in the success level found with patients requiring lower adds. This increased add effect might well improve the success of multifocal GPs. Unwanted effects may also occur from having a wider range of add powers in the same small space, so we may need to learn which designs benefit most from the increased power effect.
Contamac The first high-index GPs approved by the FDA were introduced by Contamac: Optimum HR 1.51 and Optimum HR 1.53 materials. Most GPs have had index of refractions in the 1.41 to 1.46 range, so these two materials are a definite step up. Both lenses also have low specific gravities, making them even better at reducing lens mass. The higher-index material has a lower oxygen transmission (Dk of 27 for HR 1.53; Dk of 50 for HR 1.51).
Paragon Vision Sciences The FDA recently approved Paragon HDS HI 1.54, now the highest-index GP material available. It is a low-specific gravity material that allows further weight reduction compared to most GPs, in addition to reduction achieved by the increased index of refraction, allowing less material to achieve the same refractive effect. CLS
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.