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S. A. McFadden, R. Cuskelly; Short Periods of Plus Lens-Wear Overrides the Myopiagenic Effects of Minus-Lens Wear in Guineapigs. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1532.
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© ARVO (1962-2015); The Authors (2016-present)
In chicks, very brief periods of positive spectacle lens-wear completely overshadows the myopiagenic effect of wearing minus lenses for the rest of the day. It is just as effective as inducing hyperopia as brief periods of plus lens-wear with normal vision without lenses for the rest of the day1. The amelioration of the effect of negative lenses by a plus lens is greater than a plano lens1. In contrast, in monkeys, briefly replacing a negative lens with plano lens is more effective than replacing it with a +4.5 D lens2, and in tree shrews, 45 mins of +3, +4 or +5D lens-wear, reduces the myopia arising from -5D lens-wear, but the vitreous depth is still greater in the lens-wearing eye and it does not develop relative hyperopia, and the potency is less than that provided by a plano lens substitution3. To determine if this is a chick-o-centric phenomena, we tested the potency of plus lenses in counteracting minus lenses in the near adolescent guinea pig.
Guinea pigs wore -4D lenses on one eye from day 10-22 continuously for a 12 hr day (n=8), or had +4D lenses substituted during two 1 hr periods (n=6), or wore +4D and -4D lenses for an equal amount of time in 3 hr periods (n=8). At 22 days of age, refractive error (streak retinoscopy) and corneal power (infrared videokeratometry) were measured in awake cyclopleged animals, and ocular parameters determined using high frequency ultrasound under anaesthesia.
After 12 days, continuous minus lens wear resulted in relative myopia (-1.41±1.3D) and longer axial lengths (+50±17 µm) as expected4. In contrast, every guinea pig which had +4D lenses substituted for 1 hr periods had shorter axial lengths (mean, -36±17µm) and on average were relatively hyperopic (+1.04±0.6D). This induced hyperopia required short periods of exposure, as longer 3 hr periods were not as effective in counteracting the myopia from minus lens-wear (reduced to -0.19±0.7D).
Contrary findings between chicks and mammals may be related to the timing of lens-exposure. If children are like guinea pigs, then we predict that the equivalent of multiple short periods of positive spectacle lens-wear will be effective in counteracting minus lens-wear, while longer periods will be less effective.1. Zhu X, Winawer JA, Wallman J. Invest Ophthalmol Vis Sci. 2003 44(7):2818-27.2. Kee C-S, Hung L-F, Qiao Y, Ramamirtham R, Winawer JA, Wallman J, Smith EL, ARVO Abstract 2925, 2002.3. Norton TT, Siegwart JT Jr, Amedo AO. Invest Ophthalmol Vis Sci. 2006 47(11):4687-99.4. McFadden SA, Howlett MH, Mertz JR. Vision Res. 2004 44(7):643-53.
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