Prescribing for Presbyopia
Evolution in Fitting a Hybrid Multifocal
BY THOMAS G. QUINN, OD, MS, FAAO, & ROBERT L. DAVIS, OD, FAAO
One option for presbyopes whose corneal toricity matches their vertexed spectacle astigmatism is the Duette Multifocal (SynergEyes). This lens is significantly different from the original SynergEyes Multifocal in both design and optics.
The Duette Multifocal offers a highly oxygen-permeable central GP portion (Dk=130) combined with a silicone hydrogel skirt. It is available in six base curves and three skirt curves (flat, medium, and steep). The GP portion incorporates edge lift, elevating the rigid/soft junction off of the cornea. This is designed to counteract any tendency for flexure and to enhance lens movement.
Fitting Duette Multifocal
The Add Rather than employing a dedicated central spherical add zone into the optics of the rigid portion of the lens as in the original SynergEyes Multifocal, the Duette Multifocal employs a center- near aspheric optic. It is standard on all Duette Multifocal lenses, so no add power needs to be specified when ordering the lens. It is necessary to specify add zone size, available as small or large. If the spectacle add power is +1.75D or less, choose a small add size. Otherwise, choose a large add zone size.
Determining Lens Power Over-refraction is used to determine lens power. It also provides information on central lens fit, making fluorescein evaluation unnecessary. The final lens power is expected to be –0.50D to –1.50D more than the vertexed spectacle lens sphere power.
Figure 1. Cross section and pachymetry results with a flat skirt.
Figure 2. Cross section and pachymetry results with a steep skirt.
The Skirt Curve It had been previously thought that steepening the skirt curve lifted the central GP portion off of the cornea. Recent work by Dr. Davis suggests that this is not the case with many patients (Figures 1 and 2).
The revised recommendation is to start with a flat skirt curve on one eye and a medium skirt on the fellow eye. A too-steep skirt will feel comfortable initially, but over time will tighten and cause a stagnation of tears, leading to hyperemia and metabolic distress.
How do you know which skirt curve is right? After 10 minutes of settling, the flattest skirt that provides comfort, centration, and good movement (about 1mm upon a full blink) is the best. Any wrinkling at the edge indicates a too-flat skirt. CLS
|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 has been an advisor or consultant to Alcon, B+L, Ciba Vision, CooperVision, and Vistakon, has received research funding from Alcon, AMO, B+L, Ciba, CooperVision, and Vistakon, and has received lecture or authorship honoraria from Alcon, AMO, B+L, CooperVision, GPLI, SynergEyes, and Vistakon. You can reach him at email@example.com. Dr. Davis is cofounder of Eye-Vis Eye and Vision Research Institute. He practices in a suburb outside Chicago. He has received research funds from SynergEyes, CooperVision, and B+L and has a proprietary interest in SpecialEyes and Alternative Vision Solutions.|