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A. Seidemann, F. Schaeffel; Closed– and open loop convergence and accommodation as measured with the PowerRefractor in emmetropic and myopic subjects. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2751.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It is still not yet clear which visual cues stimulate myopia development during near work. A common hypothesis is that accommodation errors during reading impose small amounts of negative defocus, sufficient to drive axial eye growth. We have used the PowerRefractor to detect possible differences in the accommodation–convergence crosslink in myopes and emmetropes. Methods: Closed– and open–loop convergence and accommodation were continuously recorded at 25 Hertz sampling rate in 5 myopic students (wearing their spectacles; average refractions: –3.83 ± 1.6 D) and 5 emmetropic students (–0.042 ± 0.25 D). During the measurements the subjects read small letters at different distances under mono– and binocular viewing conditions, or read monocularly over a period of 10 minutes at 3 D distance. The effect of reading on the open loop AC/A ratio and on the dynamics of accommodation was also studied. Results: After consideration of the individual angles kappa and Hirschberg ratios, the PowerRefractor provided reliable data on both accommodation (resolution about 0.1 D) and convergence (resolution about 0.9 deg). Open loop convergence (during monocular reading at 3 D target distance), was twice as high in the myopic (13.59 ± 3.11 deg) as in the emmetropic (6.55 ± 2.85 deg) group. These differences persisted during sustained reading and there was also no effect of reading on the amplitudes of convergence and accommodation, AC/A ratios, or on velocity of accommodation, although some individuals showed adaptation in different directions. Conclusions: The results confirm that there are differences in the accommodation–convergence crosslink between myopes and emmetropes, which show up most clearly under open loop conditions for convergence, and could affect accommodation errors. The PowerRefractor appeared to be a useful tool to detect these differences.
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