pediatric and teen cl care
Soft Bifocal Contact Lenses for Myopia Progression
BY JEFFREY J. WALLINE, OD, PHD, & MARJORIE J. RAH, OD, PHD
Animal studies have shown that induced refractive error can alter the growth of the eye. For example, convex lenses in front of primate eyes focus light anterior to the retina, and the growth of the eye slows. Alternatively, concave lenses focus light posterior to the retina and result in faster eye growth. For many years, it has been believed that the focus of light in the macular area regulated eye growth. However, attempts to focus light properly on the macula, either through bifocal spectacles or undercorrection of myopia, have failed to slow myopic eye growth.
Recent animal studies indicate that the peripheral retina may influence ocular growth much more than previously thought. Monkeys reared with peripheral deprivation and clear central vision showed eye growth that was outside the normal range. Even after the maculas were oblated, the eyes still emmetropized.
Primates reared with foveal ablation also emmetropized when provided unrestricted vision, and had abnormal eye growth when the vision was deprived. Primate eyes therefore respond as usual, even when the macula is nonfunctional.
Lenses and Myopia
How are these findings relevant to bifocal soft contact lenses and myopia progression?
Two independent studies have shown that corneal reshaping contact lenses slow the growth of the eye in myopic children. These contact lenses provide clear central vision, but light is focused anterior to the retina peripheral to the macula. Currently, the most recognized theory regarding the myopia control effect of corneal reshaping contact lenses is myopic peripheral optical blur.
Figure 1. Topography of a cornea following corneal reshaping contact lens wear (left) and an eye wearing a soft bifocal contact lens with a distance center (right).
Soft bifocal contact lenses with a distance center may provide a similar optical profile as do corneal reshaping contact lenses, so, in theory, they should also slow the growth of the eye. Figure 1 shows topographical evidence of the similarity of effect on the front surface of the eye (corneal reshaping contact lenses) or the contact lens (soft bifocal contact lens).
Anecdotal evidence regarding this theory was presented by Aller and colleagues (2008). Two identical twins showed decreased eye growth after the first year of wearing soft bifocal contact lenses with a distance center and concentric near zones. Dr. Aller also presented evidence from a randomized clinical trial at the 2008 International Myopia Meeting that indicated an almost five-fold decrease in axial growth over one year for soft bifocal contact lens wearers compared to single vision contact lens wearers.
While there is still much to learn about the role of peripheral optics in eye growth regulation, preliminary results provide an interesting story that may lead to a vastly improved body of knowledge about myopia and possible myopia control or even preventive agents. CLS
For references please visit www.clspectrum.com/references.asp and click on document #160.
Dr. Walline is an assistant professor at The Ohio State University College of Optometry, where he conducts studies of pediatric contact lens wear. He is also a consultant or advisor and has received research funds from Paragon and Vistakon. Dr. Rah is a staff optometrist at the Massachusetts Eye and Ear Infirmary Contact Lens Service where she specializes in medically necessary and other advanced contact lens designs.