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V. Sreenivasan, E. L. Irving, W. R. Bobier; Effect of +2D Lenses on the Variability of Accommodative Response in Myopic and Emmetropic Children. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3975.
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Higher variability of accommodation response (VAR) has been reported in myopes 1, 2 and speculated to be a risk factor for the progression of myopia. We wanted to investigate whether near adds are capable of reducing accommodative variability and also determine the influence of near phoria on the VAR in myopic and emmetropic children.
18 myopic (-1.90 ± 0.3D) and 14 emmetropic children (0.5 ± 0.12D) between 7 and 14 years were examined. All emmetropic children had normal near phorias (EN, -3.18 ± 0.7Δ) at 33 cm. Myopic children were further classified into "normophores" (MN, -3.12 ± 0.9Δ; N=9) or esophores (ME, 3.2 ± 0.8Δ; N=9) based on their habitual near phoria. Binocular steady-state measures of accommodation were obtained before and after a 20 minute near task for 5 sec using a PowerRefractor (Multichannel Co) while children fixated a target (33 cm) with and without +2D lenses. VAR was defined as the standard deviation of the accommodative response across the 5 sec period.
In the no-add condition, myopic children showed significantly greater (P<0.01) pre-task accommodative lags (EN = 0.7± 0.09D; MN= 1.0± 0.10D; ME= 1.48± 0.06D) and VAR (EN = 0.20± 0.01D; MN=0.30± 0.03D; ME= 0.34± 0.03D) compared to emmetropes. Accommodative lags showed poor correlation with VAR (r = 0.19, P>0.1) and did not account for the greater variability observed in myopes. Introduction of +2D lenses significantly reduced (P<0.05) the VAR in both myopic groups (MN= 0.21± 0.01D; ME= 0.18± 0.01D) but not the emmetropic group (EN = 0.2± 0.01D; P>0.5) such that the VAR in myopic groups was equal to that of emmetropes (P>0.8). The reduction in VAR through +2D lenses was maintained (P>0.5) in the myopic groups even after 20 minutes of near activity.
Variability of accommodative response is differentially affected by refractive state when the stimulus to accommodation is decreased with near addition lenses. It appears that near adds are capable of decreasing VAR in myopes. If accommodative instability creates a variable retinal image that drives myopia, then progressive adds might be beneficial.1. Langaas T, et al. Optom Vis Sci. 2008;85:37-48.2. Harb E, et al. Vision Res. 2006; 46:2581-92.
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