Abstract
Purpose:
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.
Methods:
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.
Results:
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).
Conclusions:
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.
Keywords: 605 myopia •
677 refractive error development •
547 hyperopia