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Jason Shen, Frank Spors, Don Egan, Chunming Liu, Xiangyun Liu; A pilot study on effects of sustained accommodation on the optics of the human eye. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6013.
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Myopia often presents and progresses throughout the school years and it has been hypothesized that high levels of near work may contribute to its development. The optics change during near work; for example, lag of accommodation might be related to myopia progression. This study is to investigate the possible changes of the optics of the eye during the sustained near work.
A commercial Shack-Hartmann aberrometer was modified to be an open field instrument in order to achieve unrestricted visual field. Twenty-one low myopes were recruited into the study with only their left eyes being measured. Subjects were instructed to watch a 15 minutes long video displayed on a computer screen placed 50 cm in front of the eyes. Measurements were taken at one minute intervals while the subjects were directed to fixate on a central Maltese Cross target. Up to six-order Zernike coefficients were recorded and analyzed. Both a small sample non-parametric signed rank test and paired t-test were used for statistical data analysis.
The averaged mean spherical equivalent (MSE) refractive error decreased in the first 9 minutes at the rate of 0.06 D per minute. After 9 minutes, MSE showed more fluctuation with time. Changes of 3rd-order coma were more pronounced than changes in other higher order aberration terms. 4th order spherical aberration consistently decreased during the first 7 minutes. Compared to 2nd order defocus change, higher order aberrations had no significant impact to the changes of the optics of the measured eyes within 15 minutes of accommodation (p > 0.05).
The accommodation of the eye decreases first, but later shows more fluctuation with sustained near work. Optical changes in the eye with prolonged near work appear to be mainly caused by the changes in the 2nd order defocus term rather than by higher order wavefront errors in the eye.
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