Refractive Focus

Soft Bifocals: The Next Step in Slowing Myopia Progression?

By David A. Berntsen, OD, PHD, FAAO

Earlier this year, Refractive Focus columns have discussed studies in which attempts were made to slow myopia progression using bifocal spectacles and orthokeratology. The first ortho-k randomized clinical trial was just published and showed a 43-percent reduction in axial growth over two years (Cho and Cheung, 2012), confirming the 33-percent to 56-percent reductions previously reported by non-randomized studies (see Refractive Focus from February 2012). It has been suggested that orthokeratology may reduce axial eye growth due to peripheral myopic defocus induced by the change in corneal shape caused by ortho-k lenses (Kang and Swarbrick, 2011).

Long-term (3+ year) clinical trials are still needed to determine the long-term effect of peripheral myopic defocus on myopia progression in children. That being said, if peripheral myopic defocus does in fact slow myopia progression, what about utilizing soft lens designs to induce peripheral myopic defocus?

Soft Contact Lenses an Option?

Though there used to be concerns that soft contact lenses might result in “myopic creep,” the results from a large, randomized clinical trial found no difference in myopia progression over three years between children wearing single vision spectacles and those wearing single vision soft contact lenses (Walline et al, 2008). Further work has also shown that children are just as successful at being fitted with soft contact lenses as teenagers are (Walline et al, 2007). Given that children are able to successfully wear soft contact lenses, it is no surprise that several studies have begun investigating whether optical designs that cause a myopic shift in peripheral defocus can slow the progression of myopia. Because contact lenses move with the eye, they are much preferred over spectacles for consistently delivering an optical treatment designed to influence defocus across the retina.

Several studies have examined the effect of commercially available spherical soft contact lenses on peripheral defocus. Similar to single vision spectacles, studies have reported that soft spherical contact lenses result in peripheral hyperopic defocus (Shen et al, 2010; Kang et al, 2012), though peripheral myopic defocus has been reported in eyes that have high amounts of myopia (Kwok et al, 2012). If peripheral hyperopic defocus stimulates eye growth, soft bifocal contact lenses that result in a myopic shift in defocus while still providing clear central vision could potentially slow myopia progression (similar to the effects reported by studies utilizing orthokeratology).

Animal studies have demonstrated that retinal regions are able to respond to local defocus signals and that peripheral hyperopic defocus can accelerate eye growth (Smith, 2011). Recently published work in chicks not only provides support for lenses designed to reduce peripheral hyperopia, but also provides animal-based results supporting the study of concentric ring bifocal designs for myopia control (Liu and Wildsoet, 2012). In fact, early studies in children have utilized both lens designs (bifocals with peripheral plus power and concentric ring bifocal designs) to try to slow myopia progression.

Previous Soft Bifocal Studies

Research evaluating soft bifocal contact lens designs is in the early stages. There are currently no large-scale, long-term, randomized clinical trials published in the peer-reviewed literature that have utilized a soft bifocal contact lens. However, the results of several smaller and/or short-term clinical studies (both randomized and non-randomized) have been presented at research meetings (Table 1). Because several studies are available only in abstract form, full details of the study design and methods are not available; however, the preliminary data support a larger investigation of soft bifocal contact lens designs as a potential means of slowing myopia progression in children.

Two studies published in the peer-reviewed literature in 2011 utilized soft contact lenses designed to create myopic defocus. Sankaridurg et al (2011) reported a one-year study in which children were fitted with a center-distance soft contact lens that progressively increased in plus power up to a +2.00D add in the periphery. Single-vision-spectacle-wearing children matched for several factors including age, gender, and refractive error served as the control group. After one year, myopia progression in the group wearing the novel soft contact lenses was 0.29D (34 percent) less than that of the spectacle-wearing group, and eye elongation was 0.13mm (33 percent) less for the soft contact lens group. Though children in this study were not randomly assigned to one of the two groups, these data provide preliminary evidence that center-distance soft bifocal lens designs that increase in peripheral plus power warrant further investigation to determine whether such designs can be optimized to increase their efficacy.

Anstice and Phillips (2011) utilized a center-distance soft contact lens design in which concentric zones simultaneously created 2.00D of myopic defocus. In their study, one eye of each myopic child was randomly assigned to wear the concentric zone lens while the other eye wore a standard, single vision soft contact lens. After 10 months, the eyes wearing the concentric zone lens had progressed 0.25D less (37 percent) compared to the fellow eyes and had grown 0.11mm less (49 percent) compared to the fellow eyes. The lens design worn was switched between eyes for the next 10 months, during which time the eyes wearing the concentric zone contact lens again grew more slowly than did the fellow eyes wearing the single vision soft contact lens.

Further Investigation is Warranted

These two studies, when combined with others recently presented at research meetings (Table 1), provide promising evidence supporting the continued investigation of soft bifocal contact lens designs in long-term clinical trials. Soft bifocal lenses and orthokeratology both show promise, and each lens type has advantages and disadvantages. Orthokeratology provides peripheral myopic defocus during all waking hours, whereas a soft lens provides this benefit only when it is being worn during the day; however, soft bifocal contact lens designs may be able to provide more peripheral myopic defocus than orthokeratology can for eyes that have low amounts of myopia (e.g., emerging myopic children).

There also is currently not a rapid and easy way for clinicians to measure peripheral refractive error and peripheral defocus to determine which bifocal lens design and add power provides the most favorable optical profile for a particular child, forcing a one-size-fits-all approach for most clinicians. While studies continue to investigate whether optical designs can be optimized to consistently slow myopia progression over multiple years, the currently available research provides us with useful information to aid us in educating our patients regarding what is known about the options currently available. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #203.