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Study results suggest soft contacts should slow myopia progression
In turn, spectacle wear might be expected to exacerbate it, a researcher says.
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A recent study found that correcting the on-axis refractive error in moderate to high myopia with conventional spectacle lenses resulted in hyperopic defocus in the peripheral retina, while correcting the same eyes with conventional soft contact lenses resulted in significant myopic defocus in the periphery.
“If the refractive status of the peripheral retina does influence myopia progression, then these results suggest that myopia progression should be slower with conventional contact lens wear than with conventional spectacle wear,” John Phillips, MCOptom, PhD, one of the study’s authors, told Primary Care Optometry News.
“However, previous studies comparing myopia progression with conventional spectacles and conventional contact lenses have reported no such difference. Something doesn’t add up. Either the peripheral refractive status is not as important as some have suggested, or we need to look more carefully at progression with spectacles compared to contact lenses,” he said in an interview.
John Phillips
The 11 subjects included in the study had myopia of at least -5.00 D spherical equivalent measured at the spectacle plane, astigmatism of no more than -1.50 DC, best corrected Snellen acuity of 6/7.6 and no ocular pathology or contraindications to contact lens wear. The researchers measured ocular refractions with an autorefractor when the patients were uncorrected, corrected with spectacles and corrected with contact lenses, on-axis and off-axis out to 30° in 5° steps in the nasal and temporal retina.
Upon conclusion of the study, the researchers observed a highly significant shift from hyperopic relative peripheral refraction (RPR) to myopic relative peripheral refraction when the on-axis refraction was corrected with contact lenses compared to both the uncorrected and spectacle corrected states (F2,26 = 31, P < .0001, and F2,26 = 43.14, P < .0001, respectively).
Clinically, these results suggest that if peripheral refraction influences myopia progression, then contact lens wear, which produced significant myopic defocus in the peripheral retina, would be expected to slow myopia progression, Dr. Phillips said. In addition, the hyperopic peripheral refractions associated with spectacle wear might be expected to exacerbate myopia progression.
“In addition, the results have implications for research,” he said. “Investigations into novel optical methods for slowing myopia progression based on manipulation of peripheral refraction must account for the peripheral effects of their control management. Given the difference in peripheral refractions between spherical spectacles and soft contact lenses in our study, it would be prudent to use spherical spectacles as a control when testing a novel spectacle lens design, and likewise to use spherical contact lenses as a control when testing novel contact lens designs.
“Failure to account for the peripheral effects of the control could artificially exaggerate or diminish the benefits of any novel management simply because of the peripheral characteristics of the lens modality used as control,” he added.
“The next steps depend on whether manipulating peripheral refraction really turns out to be an effective way of slowing myopia progression. We have suggested that dual-focus lenses, which create two focal planes across the peripheral and central retina, may be the way to go,” Dr. Phillips said.
A previous study published in Optometry and Vision Science in March corroborated the findings that conventional contact lenses produce myopic defocus in the peripheral retina.
In that study, data were collected on 10 subjects with a mean spherical refractive error of -8.31 D. On- and off-axis refractions were measured in primary gaze, with and without a contact lens, every 5° out to 20° horizontally in the nasal and temporal retina. They also measured eye size with partial coherence interferometry on-axis and off-axis.
The authors found that changes in the off-axis eye shape accounted for most of the change in absolute uncorrected refractive error with eccentricity, as opposed to off-axis changes in the anterior eye.
“A number of lens modalities, including dual focus contact lenses, orthokeratology lenses and radial refractive gradient spectacle lenses, have been investigated as methods for modifying peripheral refractions with the aim of reducing childhood myopia progression,” the study authors said. “If peripheral myopic defocus inhibits myopia progression, then the peripheral myopic defocus present with standard spherical soft contact lenses may provide a degree of protection against myopia progression in patients with higher degrees of myopia.” – by Daniel R. Morgan
References:
- Backhouse S, Fox S, Ibrahim B, Phillips JR. Peripheral refraction in myopia corrected with spectacles versus contact lenses. Ophthalmic Physiol Opt. 2012;32(4):294-303; doi: 10.1111/j.1475-1313.2012.00912.x.
- Kwok E, Patel B, Backhouse S, Phillips JR. Peripheral refraction in high myopia with spherical soft contact lenses. Optom Vis Sci. 2012;89(3):263-270.
For more information:
- John Phillips, MCOptom, PhD, can be reached at the Department of Optometry and Vision Science, The University of Auckland, 85 Park Road, Grafton, Auckland, New Zealand 1023; +64 9 923 6073; email: j.phillips@auckland.ac.nz.
- Disclosures: Dr. Phillips is the named inventor on a patent relating to a dual focus contact lens design (US 7,997,725).