letters to the editor
Response to Hybrid Myopic Shift
We appreciate your coverage of the Duette HD (SynergEyes) lens in the June 2012 issue of Contact Lens Spectrum; however we would like to comment on the article “Myopic Shift Secondary to Hybrid Lens Wear” by Dustin Gardner, OD, and Aaron Zimmerman, OD, MS, FAAO. The details in this report make it likely that the Duette HD lenses described may not have been fit correctly. Our data demonstrates that when properly fit, Duette HD lenses do not mold the cornea, but instead produce stable results in patients who have moderate to high amounts of astigmatism, myopia, and hyperopia.
Although we encourage singlecase reports, we are dismayed that data from a single patient is presented to support a new purported use of the Duette HD contact lenses for corneal molding. Further, while we realize that myopia control is a hot topic in the eyecare community, prescribing Duette HD lenses for this purpose is an off-label use of the product and is strictly a decision of the practitioner. This lens is FDA cleared specifically for the correction of myopia, hyperopia, and astigmatism and not corneal reshaping.
The authors indicate that they followed the Duette HD nomogram for initial selection of base curves based on the assumed K readings. However, the Duette HD fitting guide specifically requires adjusting the base curve selection via an over-refraction by determining whether it is within the range of 0.25D to 1.00D more minus than the spherical component of the patient's manifest refraction. The authors may have done this, but they make no mention of it. Absent that, we believe that it was not done even after the patient presented with complaints at the two-month point, and the authors simply took the patient out of the lenses. It is therefore impossible to determine the exact etiology of the reported findings. We would also point out that the Duette HD fitting guide specifically recommends against using Sim Ks from a corneal topographer for choosing base curves.
The base curve of the Duette HD lens is prolate in shape so that it closely matches the asphericity of the cornea. Because of the prolation, the difference between the lacrimal power of base curve increments that we provide is approximately 1.00D. The purpose of the skirt is to elevate the GP segment of the lens completely off the cornea to increase comfort and to minimize molding. Because of that, an over-refraction showing the need for a contact lens power that is greater than 1.00D more minus than the glasses prescription indicates that the fit of the lens is one base curve steeper than the best fit for the cornea. For this case, the topographic and power changes, along with the patient complaints at the two-month point, indicate that a change in base curve, skirt curve, or both were indicated.
We agree that the evidence in this report shows corneal molding, but not because of lens design. If the GP segment is not adequately supported above the cornea, corneal molding may occur as it did in this case. This could take the form of corneal steepening if the base curve is too steep or if the skirt curve is too flat. Corneal flattening may occur if the base curve and skirt curve are too flat. The occurrence of a −0.50D to −0.75D change in refraction after two months of Duette HD wear combined with the report of midperipheral flattening and a corneal compression ring indicate that the lens was not properly fit—the base curve radius was too steep, the skirt curve was too flat, or both.
In summary, this case shows the effects of an improperly fit lens that produced temporary, short-lived, and reversible corneal molding.
Paul A. Kusy, OD, MS, FAAO
Manager, Clinical Research and Design
SynergEyes, Inc., Carlsbad, Calif.
Dr. Zimmerman and Dr. Gardner's Response:
We thank Dr. Kusy and SynergEyes, Inc. for their comments and appreciate the opportunity to respond. Dr. Kusy correctly addressed the cause of the corneal molding as resulting from a lessthan-perfect fit and not from a lens design flaw. We agree that the lens itself is not in any way flawed; however, this case illustrates how an imperfect fit with Duette HD was associated with a noticeable change in refractive error and corneal curvature.
This case report came from one of the first patients whom we fit with the Duette HD lens. The patient's keratometry values were at the flat end of the manufacturer's available parameters, and the fitting nomogram indicated that we should use the flattest base curve available. The initial lens showed slightly excessive touch in the periphery, so we selected the steep soft skirt. The steeper skirt provided a better fit, which was thought to be acceptable.
The over-refraction for the right and left eyes were −1.00D and −1.50D more than the spectacle sphere, respectively. However, the nomogram issued with our fitting set did not make reference to the over-refraction criteria. We were made aware of this criteria when we received the Duette Multifocal set with an updated fitting guide, which we had not yet received at the time that we submitted this article.
Based on the over-refraction criteria, it is now clear that we would have correctly identified that the patient simply was not a good candidate for the selected base curve. The appropriate next step was choosing a flatter base curve, which is not available in the Duette HD design; therefore, the lens was not a good option for this particular patient.
We also agree with Dr. Kusy that using a product for an off-label purpose requires evidence of its safety and efficacy, and a single case report is not sufficient. This comment was meant to be thought-provoking rather than a clinically acceptable method for managing low levels of hyperopia. We have not had, and do not have, any intentions to utilize the Duette HD lens design in this manner.
The purpose of this case was to illustrate the results of a lens fit that was perceived to be clinically acceptable. Through more detailed analysis and review of the evaluation of lens fit, we were able to demonstrate the outcome and complications of a fit that was less than ideal.
|PLEASE SEND YOUR LETTERS TO:|
|Editor, Contact Lens Spectrum |
323 Norristown Rd., Suite 200
Ambler, PA 19002
Fax: (215) 827-5390
Or e-mail letters to:
We reserve the right to edit letters for clarity and space.