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CONTACT LENS CASE REPORTS

MULTIFOCAL SOFT LENS DESIGNS FOR MYOPIA CONTROL

An ever-growing number of eyecare professionals around the world are utilizing multifocal soft contact lenses to slow the progression of myopia in children (currently an off-label use in the United States). However, to date, it is unclear as to what the optimum soft lens design and add power might be to provide the greatest therapeutic effect.

Animal studies by Tse et al (2011) and Benavente-Pérez et al (2014) appear to indicate that the greater the area of plus power presented to the retina, the greater the myopia controlling effects. Theoretically, a lens with a greater add power and/or larger add area would provide the most robust peripheral defocus stimulus.

It is difficult to “classify” the optics of multifocal soft contact lenses because of many subtle nuances that manufacturers incorporate for marketing and/or patent differentiation. However, if we distill the optical features of a myopia control soft lens, we come down to two fundamental components: a central distance optic of approximately 2.0mm designed to provide a clear foveal image, and a midperipheral “plus zone” from approximately 2.0mm to 8.0mm to converge the peripheral image shell.

Figure 1A shows the position of the image shell when a myopic child is corrected with traditional spectacle lenses. Figure 1B illustrates the child’s eye corrected with a low add power of approximately +1.50D. In this situation, the image shell is converged to a small area (spot) on the retinal plane. Figure 1C shows the myopic child’s eye with a higher midperipheral add power in which the peripheral light/images are converged anterior to the retina, with an enormous blur circle projected onto the peripheral retina.

Figure 1. The image shell in a myopic child corrected with traditional spectacle lenses (A), the image shell associated with a low add power multifocal lens (B), and the image shell with a high midperipheral add power (C).

Differentiated Designs

There are endless theoretical designs that can provide a clear foveal image and peripheral plus power to a child’s eye. At Pacific University, we are looking at three different concentric lens designs that all provide a 2.0mm central zone for distance acuity and various add powers from +1.00D to +4.00D (Figures 2 to 4).

Figure 2. Concentric Aspheric Addition Design

Figure 3. Concentric Linear Addition Design

Figure 4. Concentric Constant Addition Design

The most striking feature of these three lens designs is the “area” over which that add power is present. Animal studies and clinical impressions have led us to believe that peripheral converging power and the physical area of the retina involved in the “process” are perhaps two critical components to effective myopia control in children. CLS

For references, please visit www.clspectrum.com/references and click on document #258.