Contact Lens Design & Materials
Controlling Myopia: Here Yet?
BY NEIL PENCE, OD, FAAO
Myopia control lenses have been much talked about. Because no lenses in the United States have an approved indication for myopia control, some ask what we can do now for patients. First, let’s review the principle behind myopia control lenses and touch on possible options today.
Current Lens Options
Myopia control lenses are designed to eliminate relative peripheral hyperopic defocus, thought to be related to myopia progression (Smith, et al, 2009). When corrective lenses are used to eliminate myopic refractive errors at the fovea, they generally create a slightly hyperopic focus in the periphery. This may serve as a stimulus for the eye to move the retina back to lessen this peripheral defocus, leading to continued myopia progression.
Several patented designs to counteract this employ a “dual focus” system. The central portion of the lens is used to correct distance vision, and the midperiphery of the lens lessens/eliminates the peripheral hyperopic defocus in a concentric design. It may employ two spherical zones or an aspheric design to provide more plus correction in the periphery. The success of this in slowing myopia progression is still under investigation, but it appears promising (Sankaridurg, 2011).
Overnight corneal reshaping lenses are GP lenses used to lessen the need for lens wear during the day. Overnight, lenses flatten the central cornea and steepen the midperipheral cornea, which causes a more plus refractive correction relative to the center. This induced midperipheral myopic defocus may be useful in preventing myopic progression (Kakita, 2011). This occurs using standard overnight corneal reshaping lenses, so it would not be an off-label use for myopes. Eventually the effect may be enhanced with dedicated myopia control designs that feature modified optic zones or reverse curves.
While GP ortho-k lenses reshape the cornea to provide the desired effect, other currently available lens designs appear to be similar to the “dual focus” myopia control lenses. Another name for “dual focus” would be “bifocal.” Any contact lens multifocal with a center-distance design creates a relative plus or hyperopic focus in the periphery. This in turn may eliminate the peripheral hyperopic defocus believed to spur myopic progression.
Multifocal lenses on young myopes would be considered an off-label use. This is also true when used for young persons who have accommodative problems or high AC/A ratios, the success of which has been shown although there is no specific indication for this use (Libassi, 1985; Edmondson, 1987). Be sure to discuss this off-label use with the parents. Offer no guarantees as to the ability to stop or slow myopia progression, but rather state that the possibility exists based upon our current knowledge. If young patients are interested in wearing contact lenses, they might consider lenses of this design.
What Can We Do Now?
As we wait for myopia control lenses to be approved, you can discuss factors related to myopia progression with parents. As previously stated, overnight GP reshaping lenses or soft multifocal designs with center-distance correction might be employed, but you must clearly state that while a beneficial effect may occur, it is not possible to say at this time.
Additionally, based upon what has been reported, we can recommend that kids be given well-lighted areas for near tasks indoors and that they spend a few hours a day in outdoor activities (Jones-Jordan, 2011). With a possible positive role for vitamin D (Mutti, 2011), we can even suggest lots of chocolate milk. This cannot help but win favor with most kids, even if it does not retard their myopia progression. I wish someone had told that to my mother! CLS
For references, please visit www.clspectrum.com/references.asp and click on document #197.
|Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana. He is also a consultant to B+L, J&J Vision Care, and Alcon. You can reach him at email@example.com.|