Prescribing for Presbyopia
Centration Is Key for GP Multifocal Lenses
BY THOMAS G. QUINN, OD, MS, FAAO
Successful single vision GP lens wearers are often great candidates for multifocal GPs. When presbyopia hits, what’s the best approach to take when transitioning them into a GP multifocal?
When the Single Vision Lens Is Already Centered
If a single vision lens centers well on the cornea, just about any GP multifocal lens design should work well. The most straightforward approach may be to fit a front-surface aspheric GP multifocal, which would duplicate the back-surface design of the successful single vision lens.
Be aware that adding an aspheric front surface sometimes increases center thickness, which may impact centration. If this happens, start by contacting the lab to explore whether it is feasible to fabricate a thinner lens. If not, you may need to modify your design to improve centration.
Raising a Low-Riding Lens
To raise a low-riding GP lens, minimize center thickness. If the lens still drops, flattening the base curve and increasing the diameter can help promote attachment of the lens to the upper lid. Adding a minus carrier peripheral lens profile can further aid in this effort.
Some evidence suggests that material selection can impact GP lens centration (Quinn and Carney, 1992). Consider choosing a material with a low specific gravity when attempting to raise the lens position.
Lowering a High-Riding Lens
To lower a high-riding GP lens, increase the lens center thickness to add mass. Increasing lens size can further add to lens mass, but may also promote lid attachment, which would be counterproductive. This is most likely to occur when patients have tight upper lids that cover the superior limbus. Decreasing diameter may be a more successful approach in such cases. Thinning the peripheral profile may also help a lens drop by reducing lid attachment.
Materials that have a higher specific gravity have very little impact on lowering a high-riding lens (Carney et al, 1996).
Other Design Considerations
In some patients, a lens will persist in decentering even if you use these strategies. In my experience, high-riding lenses cause the most stubborn problems with decentration, usually because of a low, tight upper eyelid. In such cases, I’ve had the greatest success with an aspheric back-surface GP multifocal. Lenses of this design are more forgiving visually as there is not a dedicated zone on the front that must align with the visual axis. The drawback to this design is that the effective add delivered is often inadequate for more advanced presbyopes. Such patients may need to have one eye biased for near or they may need to wear reading glasses over their contact lenses for detailed near tasks.
Consider the Cornea
In cases of long-term wear of poorly centered lenses, perform corneal topography. If the results show corneal changes, it may be necessary to take the patient out of lens wear for a period of time. Allowing the cornea to normalize can help in achieving a well-centered lens.
Multiple Approaches Can Help
Manipulating the fit, choosing the right multifocal GP lens design, and rehabilitation of corneal shape can all help improve lens centration, which is vital to achieving good vision with multifocal GP lenses. CLS
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Dr. Quinn is in group practice in Athens, Ohio. He is an advisor to the GP Lens Institute and an area manager for Vision Source. He is an advisor or consultant to Alcon and B+L, has received research funding from Alcon, AMO, Allergan, and B+L, and has received lecture or authorship honoraria from Alcon, B+L, CooperVision, GPLI, SynergEyes, and STAPLE program. You can reach him at email@example.com.