Recent commercial advances in contact lens optics have centered primarily on presbyopia correction, but the control of myopia progression with novel CL designs potentially represents an even bigger consumer market.
"Research investigating different methodologies to control myopia progression by manipulating optics has been ongoing for 2 decades or longer. However, there has been a recent resurgence of interest in this area as a result of the primate work by Smith and colleagues (2005, 2007)," said Dr. Kollbaum, assistant professor, Indiana University School of Optometry, Bloomington.
Dr. Kollbaum told Optometry Times, "The outcome of these studies is that the peripheral retina may be more responsible for the regulation of eye growth than previously thought. This finding has lead to several studies evaluating potential CL technologies and even the manufacture of a commercially available soft CL in Asia (CooperVision MiSight) designed to slow myopic progression."
There have been several anecdotal reports of some success with multi-zone or bifocal CLs in controlling myopic progression. In one such report, Aller and Wildsoet reported on a pair of identical twins with near esophoria in which use of bifocal CLs in one twin reduced myopia progression by roughly 1 D in 1 year.1
This approach is based on the theory that reduction of near esophoria increases accommodative accuracy, leading to decreased lag of accommodation, decreased hyperopic defocus, and ultimately a reduced stimulus for ocular growth, he explained.
In a larger unpublished, prospective, 12-month, double-masked, randomized, controlled study with 78 subjects aged 8 to 18 years, Aller et al. (2006) achieved similarly promising results with bifocal soft CLs. Compared with the control subjects wearing single vision soft CLs, the subjects fitted with bifocal soft CLs had roughly 0.5 D less increase in refractive error and almost 0.2 mm less increase in axial length. Data from a subset of 47 of these patients wearing the bifocal soft CLs followed for an additional 2 years showed only minimal change in refraction (<0.25 D) and axial length (<0.1 mm) over the longer follow-up.
Playing with design
Other optical approaches aimed at reducing myopia progression are designed to optimally correct vision within the central pupil while also moving the peripheral image from behind the retina onto or in front of it.
One series of such designs from Holden, Ho, Sankaridurg, Aller, and Smith (US 2007/0296916) provides optical correction for distance within a central zone that is approximately the size of the pupil and has a higher-power peripheral zone that curves or shifts the focus of the oblique rays forward onto or in front of the peripheral retina. This technology has been licensed to CIBA Vision for use in CLs and to Zeiss for use in spectacle lenses (MyoVision).
"Zeiss reports that a study of the spectacle lenses at Sun Yet-Sen University, in China, found this design reduced myopia progression by 30% in a series of young children," Dr. Kollbaum said.