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A. Benavente-Perez, A. Nour, D. Troilo; The Accommodative Response Under Lens-Imposed Anisometropia in Humans. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3932.
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Imposing anisometropic defocus with lenses results in compensatory changes in eye growth and refractive state in several animal models. A recent study of monovision in human myopes is consistent with these studies in showing that the eye with more imposed myopia had reduced myopia progression (Phillips, 2005). This study examines the accommodative response through imposed anisometropia (IA) to understand the retinal defocus experienced under such conditions and how it may influence ocular growth.
Accommodation to several near target distances was evaluated in 11 subjects (8 emmetropes, 3 myopes) aged 22 to 32 yrs (26.1±3.4) using an infrared video photorefractor (Power Refractor, MultiChannels System). During measurements, lenses of opposite power (±1D and ±1.5D) were worn (for myopes, over their habitual correction) to impose either 2 or 3 D of anisometropia.
For 2D IA, the eye wearing the positive lens (effectively more myopic) was always better focused (mean lag -0.04±0.24 D); the effectively more hyperopic eye always had larger lags (-3.98±0.29 D). Under 3D IA, two strategies were adopted: (1) five subjects were better focused with the effectively more myopic eye and showed large lags with the effectively more hyperopic eye; (2) six subjects appeared to average the accommodative response between eyes so that the effectively more myopic eye showed a significant accommodative lead (+0.94±0.28 D) while the contralateral more hyperopic eye lagged (-2.02±0.13 D). The interocular difference in effective refraction was occasionally less than the IA suggesting that brief periods of aniso-accommodation may also be taking place. Subject refractive state and eye dominance were unrelated to any of the responses observed.
Under anisometropia of the type experienced during monovision, our results in young, accommodating subjects suggest that the relatively more hyperopic eye remains effectively hyperopic but the relatively more myopic eye may or may not experience myopic defocus during near vision. If the efficacy of monovision for myopia control in children depends on the presence of myopic defocus, it will be affected by the type of accommodative behavior exhibited in response to the anisometropic accommodative demands as demonstrated in this study.
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