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J. Tarrant, Y. Liu, C. F. Wildsoet; Orthokeratology Can Decrease the Accommodative Lag in Myopes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4294.
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To assess the effect of the change in spherical aberration induced by orthokeratology (ortho-k) on the accommodative response of young adult myopes. The underlying hypothesis being tested was that, due to the interaction between Zernike defocus and spherical aberration, the relative increase in positive spherical aberration induced by ortho-k would produce an increase in accommodation resulting in an increase in Zernike defocus.
The ocular aberrations of 28 myopic subjects, corrected with single vision distance soft contact lenses, were measured using a COAS wavefront analyzer for 5 target vergences: 0, 2, 3, 4 and 5 D. Participants were fitted with contact lenses approved for overnight orthokeratology (ortho-k) and ocular aberrations were reassessed approximately 4 weeks after the initiation of ortho-k treatment. Point spread functions were calculated from the Zernike coefficients and used in conjunction with metrics of optical image quality to determine accommodative errors for each subject and target vergence. Paired t-tests were used to compare these data sets.
Subjects showed increases in positive spherical aberration for all vergence settings after ortho-k (p < 0.001), ranging from 0.51 D (95% CI: 0.31-0.71D) for the 5 D target to 1.33 D (95% CI: 1.10-1.58 D) for the distance target. Significant increases in mean Zernike defocus post ortho-k also were observed for all target vergences: 1.34 D at distance, 0.57 D at 2 D, 0.42 D at 3 D, 0.22 D at 4 D and 0.27 D at 5 D (p < 0.05), indicating increased accommodative responses and thus decreased accommodative lags. The Zernike defocus was consistent with that needed to balance spherical aberration to produce the best image quality.
The increase in positive spherical aberration produced by orthokeratology resulted in the hypothesized reduction in accommodative lag. The latter effect of ortho-k offers an explanation for reports of slowed myopia progression with this treatment, assuming accommodative lags, a source of hyperopic defocus, drive myopia progression.
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