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Baskar Arumugam, Li-Fang Hung, Chi-ho To, Brien A Holden, Earl L Smith; Effects of the relative strength of the more positive-powered component in dual focus lenses on emmetropization in macaques. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2169.
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© ARVO (1962-2015); The Authors (2016-present)
Dual focus lenses that impose relative myopic defocus over a large part of the visual field can slow myopia progression in children. Our aim was to determine how the relative surface area devoted to the more positive-powered lens component influenced the ability of dual focus lenses to alter refractive development.
Beginning at 3 weeks of age, infant rhesus monkeys were reared with Fresnel lenses that had central 2mm zones of zero power and concentric annular zones that had alternating powers of +3.0D or 0D. The relative spatial widths of the annular zones were varied from 1:1 (i.e., equal widths) to 1:4.5 (+3D:0D) between treatment groups (n≥6 per group). The monkeys wore the treatment lenses over both eyes continuously until 151±4.2 days. Comparison data were obtained from monkeys reared with full field +3D lenses over both eyes (FF+3D, n=6) and from 34 control monkeys reared with unrestricted vision. Refractive status, corneal power and axial dimensions were assessed every 2 weeks throughout the lens rearing period.
All of the dual focus lens designs produced relative hyperopia. At the end of the treatment period, the median refractive errors for the monkeys reared with dual focus lenses that had width ratios of 1:1, 1:2, 1:3 and 1:4.5 were +5.25D, +5.19D, +4.31D, and +4.28D, respectively, which were similar to the refractive errors exhibited by animals reared with FF+3D lenses (+4.63D; p=0.22 to 0.94), but significantly more hyperopic than those found in age-matched control monkeys (+2.50 D; p=0.0002 to 0.004). The average vitreous chamber depths for the dual-lens-reared animals were also not significantly different from those found in FF +3D lens-reared monkeys (OD:+3D/pl 1:1; 9.31±0.34mm, 1:2; 9.44±0.60mm, 1:3; 9.74±0.38mm, 1:4.5; 9.55±0.25mm vs 9.58±0.32mm, respectively, p=0.18 to 0.87). In addition, there were no significant differences in either the median refractive errors (p=0.08 to 1.0) or the average vitreous chamber depths (p=0.06 to 0.71) between the dual focus lens groups.
The results demonstrate that even when the more positive-powered zones make up only about 1/5th of a dual-focus lens’ surface area, refractive development is dominated by relative myopic defocus. Overall, the results emphasize that myopic defocus distributed across the visual field evokes strong signals that can slow eye growth in primates.
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