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Baskar Arumugam, Li-Fang Hung, Chi-ho To, Earl L Smith; The effects of the relative strength of simultaneous competing defocus signals on emmetropization in infant rhesus monkeys. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3603.
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© ARVO (1962-2015); The Authors (2016-present)
The aim of this study was to investigate the effect of dual focus lenses with unequal areas devoted to competing defocus signals on emmetropization in infant monkeys.
The subjects were infant rhesus monkeys that, beginning at 3 weeks of age, were reared with Fresnel lenses that had unequal areas devoted to the two power zones. The treatment lenses had central 2 mm zones of zero power and concentric annular zones that had 33:66 area ratios for alternating powers of +3.0 D and 0 D (n=6; +3D/pl) or 66:33 ratios for powers of -3.0 D and 0 D (n=6; -3D/pl). The monkeys wore the treatment lenses over both eyes continuously until 153±3.4 days. Comparison data were obtained from monkeys reared with either dual focus lenses with approximately equal power areas (50:50 area ratios) or full field single vision lenses over both eyes (FF+3 D, n=6; FF-3 D, n=6). Refractive status, corneal power and axial dimensions were assessed every 2 weeks throughout the lens rearing period. Control data were obtained from 33 monkeys reared with unrestricted vision.
At the end of the treatment period, the median refractive error and average vitreous chamber depth for the +3D/pl lens-reared monkeys were similar to those for animals reared with FF+3 D lenses (OD: +5.19 D vs +4.63 D, p=0.23 and 9.44±0.60 mm vs 9.58±0.32 mm, p=0.65) or similarly powered Fresnel lenses that had equal areas devoted to each power (OD: +5.25 D, p=1.0), but axially more hyperopic than those for control monkeys (OD: +2.50 D, p=0.0002; VC: 9.82±0.30 mm, p=0.03). On the other hand, for the -3D/pl monkeys, refractive development was dominated by the zero-powered portions of the lenses. The median refractive error for the -3D/pl monkeys was more hyperopic than that found in the FF-3D monkeys (OD: +2.94 D vs -1.19 D, p=0.02), but similar to that for monkeys reared with Fresnel lenses that had equal areas devoted to each power (OD: +3.13 D, p=0.94) and that observed in the control animals (p=0.24).
The results demonstrate that even though the least hyperopic/most myopic power zones made up only about 1/3 of the surface area of the treatment lenses, their associated image planes dominated refractive development. Overall, the results indicate that imposing relative myopic defocus over a large part of the retina provides a strong signal for slowing eye growth.
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