Contact Lens Design & Materials
Multifocal Design Matters for Myopia Control
BY GREGORY J. NIXON, OD, FAAO
In recent years, I have noticed a substantial interest throughout the patient community in controlling myopia progression. Parents, most of whom are myopic themselves, show concern for the visual welfare of their children when they are diagnosed with myopia at a young age. We must be aware of the intervention methods to address these growing concerns. Specifically, when prescribing multifocal contact lenses as an off-label use for controlling myopia progression, choosing which multifocal design to use is critical to achieving success.
Which Method Is Best?
For many years, myopia researchers have tried to identify which intervention methods are most effective in slowing the rate of myopia progression. According to Walline (2012), most eyecare practitioners consider a 50% reduction in myopia progression as the benchmark for a clinically meaningful intervention.
Most recent publications have shown that specific designs of contact lenses are far more capable of reaching this level of effectiveness compared to spectacle wear. Specifically, progressive addition lenses (PALs) have shown a reduction in myopia progression of only 16% in the Correction of Myopia Evaluation Trial (COMET) study (Gwiazda et al, 2003) and of 24% in the COMET2 study (2011).
Studies involving utilization of corneal reshaping contact lenses have shown reductions in myopia progression of 36% (Kakita, 2011), 58% (Walline, 2011), and 63% (Charm and Cho, 2013). Similar reductions of 50% have been found with the use of center-distance multifocal contact lenses (Anstice, 2011; Walline et al, 2013). Either contact lens method is a great option to help manage the epidemic of myopia progression among today’s youth.
The Science Behind Myopia Control with Contact Lenses
The key to each of the contact lens modalities described above is the optical effect induced on the peripheral retina. We have come to understand that myopia development and ongoing progression result from hyperopic defocus in the peripheral retina. Consequently, inducing a myopic defocus in the same area of the peripheral retina results in a slowing of axial elongation.
A center-distance multifocal contact lens has an annular zone in the midperiphery where the add power begins (Figure 1). This higher plus power results in the peripheral rays coming into focus in front of the retina, which provides its protective effect.
Figure 1. Design of a soft center-distance multifocal lens.
To provide the highest probability of achieving a myopia protective effect, an add power of at least +2.00D is recommended to create ample peripheral myopic defocus, represented by the green dashed line in Figure 2. CLS
Figure 2. Diagram of the peripheral optics related to myopia progression.
For references, please visit www.clspectrum.com/references and click on document #244.
Dr. Nixon is the associate dean for Clinical Services and professor of clinical optometry at The Ohio State University College of Optometry. He is also in a group private practice in Westerville, Ohio. You can reach him at firstname.lastname@example.org.