Dual-Focus Soft Contact Lenses Slow Myopia Progression in Childhood

NEW YORK (Reuters Health) Feb 03 - Results of an early phase trial indicate that an experimental dual-focus soft contact lens can reduce myopia progression in children, according to a New Zealand team.

Dr. John R. Phillips and Dr. Nicola S. Anstice at the University of Auckland explain in Ophthalmology online January 27 that while optical correction restores visual acuity, it does not stop enlargement of the myopic eye. "Thus, children with myopia remain at increased risk of ocular disease later in life."

Specifically, Dr. Phillips added in an email to Reuters Health, "The increased risk of glaucoma, retinal detachment, myopic chorio-retinal degeneration etc. in later life relates to the excessive axial enlargement of the eye that has occurred and that is associated with myopia."

Evidence from animal and human studies indicate that retinal defocus -- with the plane of focus in front to the retina -- reduces axial eye growth, but at the cost of poor acuity.

"The developing eye controls its normal growth with a feedback mechanism (within the eye) which consists of a defocus-detecting mechanism somewhere in the retina," Dr. Phillips said. "If the eye is 'too large' and the retina is 'behind' the focal plane, then a signal (unknown) is generated which influences the local remodeling of the sclera to inhibit scleral expansion and reduce eye elongation."

The researchers developed a dual-focus soft contact lens with a central zone that corrects refractive error and presents a clear retinal image, while concentric treatment zones on the lens simultaneously create sustained retinal defocus peripherally.

To see if wearing the lens would slow myopia progression, Drs. Phillips and Anstice had 40 affected children wear the dual-focus lens in one eye and a single vision distance lens in the other for 10 months, and then switch lens assignment between eyes for a second 10-month period. The children were between 11 and 14 years of age.

The mean spherical equivalent refraction (SER) was -2.71 diopters. During the first period, the mean change in SER was -0.44 diopters in eyes with dual-focus lens compared with -0.69 diopters with the single-focus lens. Corresponding mean increases in axial length were 0.11 mm and 0.22 mm, according to the report.

"In 70% of the children, myopia progression was reduced by 30% or more in the eye wearing the dual-focus lens relative to that wearing the single vision distance lens," the investigators said. Similar results were seen in the second period when the lenses were swapped.

Furthermore, visual acuity and contrast sensitivity were no different with the dual-focus lenses and the single focus lenses, and eyes wearing the dual-focus lens were able to accommodate to near targets via the central zone, the team reports.

They conclude that "sustained myopic defocus, even when presented to the retina simultaneously with a clear image, can act to slow myopia progression without compromising visual function."

Are dual-focus lenses expensive? "The lenses would be no more costly to produce than normal soft lenses (they are already commercially available in Hong Kong as MiSight lenses manufactured by CooperVision, and very recently in Australia and New Zealand)," Dr. Phillips said.

"The children will already need some sort of correction -- either glasses or contact lenses to correct their myopia anyway," he added. "These lenses are essentially ordinary daily-disposable soft contact lenses which additionally create a particular pattern of defocus (myopic defocus) on the retina, as well as allowing normal clear vision."

http://www.medscape.com/viewarticle/736807?src=mp&spon=36

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