Contact Lens Design & Materials
Continuous Improvement Principles in a Soft Multifocal
BY NEIL PENCE, OD, FAAO
The recent introduction of the PureVision2 Multi-Focal For Presbyopia lens from Bausch + Lomb (B+L) represents another example of a contact lens manufacturer continually improving its products. As technology advances, currently marketed contact lens products could conceivably benefit from various enhancements such as manufacturing improvements, design changes, or material changes.
Lens Design Improvements
The PureVision2 Multi-Focal For Presbyopia development story owes a good deal to investigations analyzing lens powers in multifocal contact lenses. Using Hartmann-Shack wavefront data, B+L researchers analyzed lens power profiles (Vogt, 2011; Hovinga, 2013; Vogt, 2013). These investigations found power distribution inconsistencies in existing soft multifocal lenses. Lenses labeled with a certain add power might have fairly different add power effects for different distance powers. Likewise, the distance lens power effect might vary from the labeled distance power within a particular add power option. This likely accounts for some of the variability in performance of soft multifocal contact lenses.
In addition to implementing changes that were designed to produce lenses that have more consistent power profiles, B+L also modified the lens design. Similar to the PureVision Multi-Focal, the PureVision2 Multi-Focal For Presbyopia is available in two add powers: high and low. The aspheric transition areas have been modified in the new lens, with the goal of enhancing intermediate vision. The power profiles of the new design seem to have a wider intermediate area in which the asphericity changes less rapidly. This should result in better performance for intermediate vision, such as computer use. The additional power added to the very center of the lens is expected to improve near vision. B+L refers to the combined result of these modifications as a 3-Zone Progressive design.
Finally, PureVision2 Multi-Focal For Presbyopia incorporates similar improvements to those of PureVision2 and PureVision2 For Astigmatism. PureVision2 Multi-Focal For Presbyopia is thinner throughout the lens compared to the PureVision Multi-Focal design—roughly 20 percent thinner in the center. Oxygen transmission is increased with the thinner lens, even though the lens material has not changed. The edge design is thinner and more rounded compared to the previous multifocal as well.
Modify Your Fitting Approach
Fitting multifocal contact lenses can be challenging, and any inconsistency in the lens power effects makes it more difficult. Even in patients who were successfully fit, we may have "gerrymandered" the powers to compensate for the unpredictable power effects.
Therefore, when refitting patients from a PureVision Multi-Focal to a PureVision2 Multi-Focal For Presbyopia, don't start with the old lens powers. Rather, base your fitting more on patients' refraction.
Change for the Better
PureVision2 Multi-Focal For Presbyopia appears to be a definite improvement over the previous PureVision Multi-Focal lens. While the lens material is unchanged, the thinner lens and the improved design result in a multifocal contact lens that is not merely new, but better as well. The more consistent power profile from lens to lens should also result in better fitting experiences and greater patient success. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #217.
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.