There is much interest and discussion surrounding the control of myopia progression in children. Myopia is increasing in prevalence, and parents are becoming increasingly concerned that their children will become very nearsighted by the time they are adults. In addition to being very blurry without correction and having to wear thick glasses to see clearly, high myopes are at a greater risk of retinal detachment, macular degeneration, and glaucoma. It is no wonder that there is a growing demand for treatments that can stop the development of myopia.
Though we have various treatment options for myopia control, we still do not know the real reason why some kids become nearsighted while others do not, or why some respond well to these treatments while others do not. Nevertheless, studies have shown that orthokeratology (ortho-k) and center-distance multifocal soft contact lenses significantly slow the progression of myopia (Si et al, 2015; Huang et al, 2016; Turnbull et al, 2016).
How the Designs Work
The current theory on how these lenses work hinges on their effect on peripheral refraction. Because progressive myopes tend to have relative peripheral hyperopia, it is thought that lenses that can induce relative peripheral myopia can help slow or stop eye growth and thereby control myopia progression (Smith, 2011; Troilo, 2016).
There are alternative theories on the relative state of the peripheral retina in myopia (Atchison et al, 2015), so this concept may not hold true. Yet, the volume of papers on the significant effect of both ortho-k and center-distance soft multifocals on myopia development (Walline, 2016) is difficult to ignore, as is the huge demand for some sort of myopia control treatment by parents for their increasingly myopic children. Both lens designs induce peripheral myopia but in different ways.
With its reverse geometry design, ortho-k changes corneal topography such that the central cornea flattens while the midperipheral cornea steepens. This is thought to increase peripheral myopia while the eye becomes emmetropic centrally. This effect is maintained throughout the day, so the presumed myopia control effect is present during all waking hours.
Center-distance soft multifocal lenses have a ring of plus power at various distances out from the center of the lens. The central distance optic zone can be varied depending on practitioner preferences and patient response. Though the optical effect is similar to that of ortho-k, the myopia control effect is only present when the lenses are on the eye. Currently, it is difficult to say how many hours children must wear their lenses to attain sufficient myopia control; so, more hours of wear are advisable until more information becomes available.
For both systems, myopia control is still not very predictable, and neither has been shown to completely stop myopia progression on a regular basis; more investigation is needed to better determine how these designs work and to further improve them to provide more predictable and effective control of myopia. In the meantime, we can offer these treatments with the caveat that they are not guaranteed to stop or even slow myopia progression for any individual child. Parents who are serious about slowing their children’s myopia may accept this for now, but better options in the future will certainly be welcome. CLS
For references, please visit www.clspectrum.com/references and click on document #254.
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry’s Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at email@example.com.