Once considered merely a refractive error, myopia has become a sight-threatening epidemic. Its incidence around the world has increased in the past 2 decades, with the highest rate and degree in the Asian population.1-3
In the United States, the incidence of myopia increased from 24% in 1971-1972 to 42% in 1999-2004.4 Individuals with myopia are more prone than others to early posterior subcapsular cataracts, myopic macular degeneration, glaucoma, retinal detachments, and retinal tears or holes.
There are several methods to treat myopia, including spectacle correction, contact lens correction, and refractive surgery. But for juvenile patients, the choices are a bit different. Treatment options for this population include orthokeratology, atropine eye drops, and daytime bifocal or multifocal contact lens wear. Experimental myopia studies and clinical research have shown that these methods can reduce the rate of axial elongation and refractive error increase associated with myopia progression.5
Bifocal and multifocal contact lenses are good options for patients who either are not candidates for or have not had successful treatment with orthokeratology. This article focuses specifically on the use of multifocal contact lenses for myopia control.
THE POWER OF THE CENTER-DISTANCE DESIGN
Soft multifocal contact lenses are available in center-distance (Figures 1 and 2) and center-near designs. Studies have shown a reduction in the progression of myopia with the use of center-distance contact lens designs.6,7 Center-distance multifocal lens designs available in the United States include the MiSight 1 day (CooperVision), the Biofinity multifocal (CooperVision), the Proclear multifocal “D” lens (CooperVision), the Acuvue Oasys for Presbyopia (Johnson & Johnson Vision), and the NaturalVue Multifocal 1-Day (Visioneering Technologies).
Figure 1. This illustration demonstrates how a center-distance multifocal contact lens design results in myopic defocus.
Photo courtesy of Pacific University College of Optometry.
Figure 2. This image shows the optics of four center-distance multifocal contact lens designs, which were imaged using a Rotlex instrument. These were all -3.00 D lenses in the highest add power available. The optic zones for the add powers vary in size. Some are strictly center-distance only and others are alternating designs.
Photo courtesy of Pacific University College of Optometry.
These soft bifocal and multifocal contact lenses provide constant distance and near correction to the treatment zone in center-distance and center-near designs when the lens is worn. Both designs remove hyperopic defocus, which causes axial elongation of the eye.
Animal studies show that the peripheral retina, not the central retina (macula), regulates eye growth.8,9 When a single-vision lens is used to correct myopia, the macula is in focus but the peripheral retina is blurry. This is known as peripheral hyperopic defocus. It is this peripheral hyperopic defocus that is thought to cause myopic progression.8
The peripheral near-vision zone of a center-distance multifocal contact lens reduces this hyperopic defocus, while the center-distance portion of the lens corrects the wearer’s vision. As a result, the peripheral light is focused in front of the retina, preventing the eye from becoming myopic by providing peripheral myopic defocus in the peripheral retina, which slows down the axial elongation of the eye.
In a prospective randomized clinical trial, Aller et al assessed the use of bifocal contact lenses (Acuvue Bifocal, Vistakon; no longer commercially available) for children with myopia age 8 to 18 years who also had esotropia fixation disparities. They reported a 72% reduction in myopia progression with the bifocal lenses in comparison with published results with multifocal spectacles.9
Walline et al observed a 50% reduction in myopia and a 29% reduction in axial length in a group of 27 myopic children age 8 to 11 years who wore Proclear multifocal “D” lenses with +2.00 D add for 2 years compared with an age-matched control group.10 Many of the candidates were not able to wear the lenses with higher add powers, which provide larger amounts of relative plus in the peripheral retina.
In an ongoing double-masked, randomized trial by Walline and colleagues, 443 children ages 7 to 11 years were randomly assigned to wear Biofinity single-vision lenses, Biofinity multifocal “D” lenses with +1.50 D add power, or Biofinity multifocal “D” lenses with +2.50 D add power for 3 years.11 This is the first study that will measure peripheral refractive error in the horizontal and vertical meridians, compare different add powers, and measure the peripheral growth of the eye.11 The study will determine whether peripheral myopia and the additional peripheral myopic defocus induced by multifocal contact lens wear affects how myopia progresses in children.
A retrospective case study by Cooper et al found that NaturalVue Multifocal 1-Day contact lenses were effective in slowing myopia in a group of 32 patients ages 6 to 19 years who were rapidly becoming more myopic before using the lenses. The study showed a halting of the progression of myopia in 81.25% of patients and myopic regression in 6.25%.12 NaturalVue Multifocal 1-Day is an extended depth of focus lens with a center-distance design with relative plus power of 8.00 D to 11.00 D at the edge of the pupil and about 20.00 D at the edge of the optical zone.
The MiSight 1 day soft contact lens is a dual focus lens with two zones for vision correction and two zones for treatments. It is the only contact lens in the United States that is approved by the FDA to manage myopia in children ages 8 to 12 years.13 In a study by Chamberlain et al,14 children were randomly assigned to wear Proclear 1 day lenses or MiSight 1 day lenses. Of 144 candidates, 109 (75.5%) completed the 3 years of the study. The mean change in axial length was 52% less in the test group than the control group, and the refractive change was 59% less. The minimum recommended wear time for myopia management is 10 hours a day for 6 days a week.12
OUR EFFORTS CAN CHANGE THE FUTURE
It is the duty of optometrists to try to reduce the current myopia epidemic for coming generations. Even a reduction of 1.00 D of myopia, regardless of a patient’s prescription, can cut the risk of myopic maculopathy by 40%.15 Multifocal contact lenses are an excellent choice for correcting myopia in our pediatric population. Not only do these lenses correct refractive error, but, in the long run, they also prevent ocular diseases such as retinal detachment, myopic maculopathy, glaucoma, and cataract.
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