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Frank Thorn, Sondra J Thorn, Ji-Chiang He; Harry Potter and the spatial spectra in English and Chinese. Journal of Vision 2003;3(9):807. doi: https://doi.org/10.1167/3.9.807.
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Purpose: Reading through ocular aberrations and defocus induced by an accommodative lag has been associated with the development of myopia. We wondered if the graphic nature of children's text can contribute to the progression of myopia. Thus we have analyzed the spatial frequency spectra of English and Chinese text intended for children in the age range that myopia is most likely to progress. We then analyzed the effect of ocular aberrations and defocus on the spatial spectra of the text's retinal images.
Methods: Harry Potter books have universal appeal to children between 7 and 13 years of age and have been translated into many languages. CT View (Sarver, Inc) was used to calculate the spatial frequency spectra of this text. The spatial spectra of its retinal image were then calculated based on different amounts of defocus and the ocular aberrations of individual children's eyes. The children, whose retinal images were simulated, were between 10 and 17 years of age and were from Beijing or Boston (He et al, 2001).
Results: Typical small amounts of ocular aberrations and defocus had little effect on the clarity of retinal images at normal reading distances. Higher amounts of aberration and accommodative defocus, which is common among progressing myopes, degraded the text. Under these conditions, a child must read through significant contrast reduction and spatial phase shifts. Thus they may rely on overall letter, word, or character shape to read fast. Spatial spectra and their retinal images were similar for English and Chinese text despite their disparate appearance.
Conclusions: The various spatial frequencies in the retinal image of the text usually have high contrast for easy reading. Higher amounts of aberrations and accommodative defocus, which are common in young myopes, causes some children to routinely read through highly degraded images of a type that is hypothesized to induce myopia.
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