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Abstract
Background
Differences in accommodation when reading Chinese, as compared to Latin, characters have been suggested to have a role in the higher prevalence of myopia in some Asian countries. Yeo and colleagues (Optom Vis Sci 2013; 90: 156‐163) found that, in Chinese‐literate children, accommodation was marginally more accurate (by less than 0.05 D), when reading Chinese text. This was attributed to the additional cognitive demand associated with interpreting the more complex Chinese symbols. The present study compared responses to single Chinese and Latin characters, while controlling for cognitive demand.
Methods
The monocular accommodative response was measured in Chinese‐illiterate adults (10 emmetropes, mean spherical equivalent: ‐0.07 ± 0.42 D, age: 29.9 ± 4.2 years; 11 myopes, mean spherical equivalent: ‐4.28 ± 2.84 D, age: 31.7 ± 4.6 years) with an open‐field autorefractor. Four Chinese and three Latin characters (approximately 1.15 degrees subtense) were individually presented on a display screen one metre away from the subject, while their vergence was varied over the range zero to 5.00 D using spectacle trial lenses. The slope and the accommodative error index (AEI) were calculated from the accommodative stimulus/response curves (ASRC).
Results
No statistically significant differences were found between refractive groups or among characters within the same refractive group in ARSC slopes (Latin: 0.87 ± 0.14 for myopes versus 0.81 ± 0.12 for emmetropes; Chinese: 0.84 ± 0.12 for myopes versus 0.85 ± 0.12 for emmetropes). No significant differences were found between characters in accommodative error index either (Latin, 0.78 ± 0.42 D for myopes versus 1.15 ± 0.72 D for emmetropes; Chinese, 0.74 ± 0.37 D for myopes versus 1.17 ± 0.83 D for emmetropes). However, accommodative error indices and accommodative errors were significantly higher for emmetropes.
Conclusion
Under controlled cognitive demand, Chinese and Latin characters elicited similar responses in both individual refractive groups. This study fails to support the hypothesis that development of myopia in some Asian populations is associated with larger lags of accommodation when reading or viewing Chinese characters.
Acknowledgements
The authors would like to thank Laura Barrios for helpful discussions about the statistics and Javier Portilla and Rafael Redondo for their help with the frequency spectrum calculation.
Most of the work described in this manuscript was presented as a poster at the European Meeting on Vision and Physiological Optics, Dublin 2012.