Contact Lens Practice Pearls
Make Room for a New Astigmatic Option
By Gregory J. Nixon, OD, FAAO
In my January 2010 column, I argued that the current eyecare landscape is approaching a time when there is a contact lens available to correct every prescription. Expanding parameter availability provides a multitude of options for patients who have astigmatism, presbyopia, dry eye, and irregular corneas.
However, fitting certain patients continues to be a challenge and requires the use of many different lens types to achieve a successful fit. Despite all of the quality options that are available with today's soft toric lenses, some astigmatic patients still experience blurred or inconsistent visual acuity.
A New Option for Astigmatism
Duette (SynergEyes) is a new hybrid contact lens that is designed and marketed specifically for astigmatic patients. Duette has a few features that make it distinct from the existing line of SynergEyes hybrids.
First, it is the only hybrid lens to offer a silicone hydrogel skirt material (hemlarafilcon A). Additionally, the GP center is also a new material (petrafocon A) that has a higher Dk (130) compared to the 100-Dk paflufocon D of the other SynergEyes lenses. More importantly, Duette has a new design feature called a junction lift area that helps the GP and GP-skirt junction areas vault the cornea to aid tear circulation and to help avoid lens adherence.
What are the Benefits?
While GP lenses have long been known to be effective options for astigmatic patients, Duette seems to combine the benefits of initial comfort, centration stability, and post-lens debris control of a soft toric lens with the visual clarity of a GP lens regardless of lens rotation. The GP center has an aspheric design that decreases aberrations to further maximize optical clarity. The Duette materials are designed to resist flexure to fit on a cornea with up to 6.00D of toricity. The GP portion is also surface treated and has a wetting angle of 38 degrees to promote lens wettability and to help enhance comfort.
How is it Fit?
Duette is fit using a diagnostic fitting set that contains a total of 15 lenses including five base curves (7.1mm, 7.3mm, 7.5mm, 7.7mm, 7.9mm), each with a flat, medium, and steep skirt radius. The initial lens to trial fit has a medium skirt curve with a base curve determined from a nomogram based on the flat K reading. The key to a successful fit is to find the skirt curve radius that provides the proper lift and results in a thin-central-clearance fluorescein pattern under the GP portion of the lens. If the initial medium skirt curve results in central bearing, use the steeper skirt radius to lift the GP portion off the cornea. Likewise, if the medium skirt results in significant central pooling, use the flat skirt radius to lower the GP into alignment over the cornea.
One significant benefit is the ability to evaluate the Duette lens using regular fluorescein rather than the high-molecular-weight fluorescein required to view the fit of hybrid lenses that have hydrogel skirts.
Adding to Your Arsenal
I still contend that we are approaching the day when there will be a viable contact lens option for nearly every patient. Therefore, it is increasingly important to be aware of all the lens options available for the myriad of fitting challenges that we face every day. The Duette lens is one new option that can provide consistent GP-quality clarity with the comfort and wearability of a soft lens for your astigmatic patients. CLS
Dr. Nixon is an associate professor of clinical optometry and director of extern programs at The Ohio University College of Optometry. He is also in a group private practice in Westerville, Ohio. He is on the Allergan Academic Advisory Board and the B+L Advisory Board. You can reach him at firstname.lastname@example.org.