multifocal SOFT CONTACT LENSes
Multifocal soft contact lenses are specially designed to have variable powers in different zones to correct presbyopia (difficulty reading with advancing age) in addition to myopia and hyperopia (farsightedness) But researchers and eye doctors are finding that conventional or modified multifocal soft contact lenses also are effective tools for myopia control similar to orthokeratology via the Peripheral Hyperopic Defocus Theory.
Peripheral Hyperopic Defocus Theory is the focussing of the peripheral light rays seen in Figures 1 & 2 behind the retina stimulating the eye to continually grow resulting in higher degrees of myopia. Figure 3 illustrates the effect on the central and peripheral light rays a result of orthokeratology and multifocal contact lenses. Studies have demonstrated a significant decrease in the progression of myopia as a result of these treatments.
In 2014, the Defocus Incorporated Soft Contact (DISC) lens slows myopia progression in Hong Kong Chinese schoolchildren: a 2-year randomized clinical trial was published. It revealed children fitted with bifocal soft contact lens had a slowing of myopia progression compared to children fitted with single vision soft contact lenses. While the results were correctly termed “significant”, the actual clinical usefulness of the 36% slowing is less clear. It does show promise and other designs may be able to increase the effect.
In November 2013, researchers in the U.S. published the results of a two-year study (Bifocal Lens Inhibition of Myopia Prevention Study) that revealed nearsighted children who wore multifocal soft contact lenses on a daily basis had 50 percent less progression of their myopia, compared with similarly nearsighted children who wore regular soft contact lenses for two years.
Children participating in the study ranged in age from 8 to 11 years and had -1.00 to -6.00 D of myopia at the time of enrollment. The study authors concluded that the results of this and previous myopia control studies indicate a need for a long-term, randomized clinical trial to further investigate the potential of multifocal soft contact lenses to control the progression of nearsightedness in children and thereby reduce risks associated with high myopia.
In June 2011, researchers in New Zealand reported on a comparison of an experimental multifocal soft contact lens and conventional soft lenses for myopia control in children. A total of 40 nearsighted children ages 11 to 14 participated in the study. The children wore the multifocal contact lens on one randomly assigned eye and a conventional soft contact lens on the fellow eye for 10 months, then switched the lenses to the opposite eye for another 10 months.
In 70 percent of the children, myopia progression was reduced by 30 percent or more in the eye wearing the experimental multifocal contact lens in both 10-month periods of the study.