Peripheral myopic defocus found to inhibit axial elongation
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Short-term peripheral myopic defocus significantly inhibited axial elongation in adults, according to a study published in Scientific Reports.
“The study shows for the first time in human subjects that peripheral myopic defocus can inhibit axial length growth attributed to the circadian rhythm,” Ryo Kubota, MD, PhD, chairman, president and CEO of Kubota Vision, told Healio. “Before the publication, such effects had only been documented with full-field defocus in human subjects, which was deemed clinically impractical.”
The study recruited 20 adult subjects with normal vision who were fitted with CR-39 prescription lenses without coating, correcting for distance refraction. The subjects viewed a full-field projected movie from 4 m away for 4 hours, with choroidal thickness measurements performed before and after the defocus sessions and axial length measurements performed intermittently during the defocus sessions. The defocus sessions were held in the morning due to the daily circadian rhythm changes in axial length and choroidal thickness.
The right eye of each subject was defocused using a Fresnel lens overlay of +3.50 D with a central clear aperture of 11.5 mm, and the left eye served as the control. Ten subjects underwent additional defocus sessions using +5.00 D of peripheral defocus. Axial length measurements and radial subfoveal choroidal scans were obtained before and after the defocus sessions.
The increase in axial length in the right eyes was significantly less than in the control left eyes for both peripheral defocus conditions (+3.50 D and +5.00 D) after the 4 hours of viewing (P < .05).
The choroids in both the test and control eyes thinned in the +3.50 D sessions, with the change slightly higher in the control eye than the test eye, but the difference was not significant. In the +5.00 D peripheral defocus sessions, the choroidal thickness in the control eyes thinned by 4 µm while the test eye thickened by 7 µm, but the differences were not significant.
According to the researchers, the results suggest that the eye’s defocus signal processing properties remain intact with only peripheral short-term myopic defocus, with the central retina moving itself forward and decreasing axial length to compensate when the peripheral image plane was moved anterior of the retina.
“These findings enhance our understanding of the interaction of biometric aspects of the eye to peripheral myopic defocus,” Kubota and colleagues wrote. “Further research is warranted to understand the underlying mechanisms of ocular biometric changes in response to various peripheral defocus applications whether the application stimuli be short term vs. long term, myopic vs. hyperopic, low vs. high dioptric magnitude, central vs. peripheral, and small vs. large (in size).”
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