prescribing for presbyopia
Combining Simultaneous and Alternating Vision GP Concepts
BY CRAIG W. NORMAN, FCLSA
Numerous discussions take place regarding the "best" type of bifocal/multifocal lens design. Most often the debate focuses (no pun intended) on the differences between simultaneous and translating vision concepts.
One view is that simultaneous vision is preferable due to the provision of optical correction at various levels, flexibility of design characteristics and improved patient comfort. Lens thicknesses are more similar to other lenses within the category either gas permeable (GP) or soft lenses. The lens mass is controllable because it is not necessary to ballast these designs as they are rotationally symmetrical.
Conversely, translating designs offer distinct areas of crisp vision, correct higher amounts presbyopia and can be more custom fit. In most cases, they need additional thickness added to the design to help them correctly position. Thus, the biggest complaints with these designs are related to excessive thickness and patient comfort due to inferior lid awareness.
Figure 1. The new X-Cel
ESSential-Solution segmented aspheric multifocal.
New Segmented Bifocal
Researchers at two leading U.S. GP lens companies have combined efforts to meld together the best of these concepts while eliminating some of the drawbacks. X-Cel Contacts and Blanchard Laboratories recently introduced the X-Cel ESSential-Solution segmented aspheric multifocal.
The posterior surface in this design is made using the aspheric S-Form technology that is the basis for Blanchard's GP and GP Xtra Multifocal. The posterior geometry specific to this new product generates about 1.00D of add power. The front surface is cut like X-Cel's Solution Bifocal with a crescent-shaped segment configuration.
Visual benefits of this combination are many. Distance vision is clear through the top portion of the lens, the aspheric posterior helps in the crucial intermediate range and the anterior segmented reading area provides crisp acuity for near tasks. Front surface segment position can be altered to many different heights customized to the patient's unique ocular measurements.
Center thickness is about 30 percent less than similar ballasted designs, even in add powers up to +3.50D. This results in decreased overall lens mass, improved lens movement and less inferior lid awareness. In fact, when we recently evaluated this lens in our practice, almost universally patients enjoyed improved comfort vs. previously worn segmented lenses. Patients presently wearing segmented designs can expect improved intermediate vision, while simultaneous design wearers can gain better reading acuity.
As with all lenses, there are some concerns. The ESSential Solution design needs to center as much as possible. Inferior positioning lenses can cause an increased need for minus correction due to the aspheric posterior surface, potentially blurring the patient at distance. Changing lens diameters can impact edge lift. Additionally, segment height position is critical to limit interference at both distance and near.
Simultaneous plus translating vision link for better performancejust the beginning of manufacturers combining technologies to improve presbyopic products.
Craig W. Norman is Director of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He is a fellow of the Contact Lens Society of America and an advisor to the RGP Lens Institute.