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F. Zhou, L.N. Thibos, D.T. Miller; The effect of cycloplegic drugs on corneal and whole–eye aberrations of the human eye . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2833.
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Purpose: Carkeet and colleagues reported recently that cycloplegic drugs can have a significant impact on higher order aberrations of the eye [J Refract Surg, 2003] which suggests that cycloplegic drugs may affect the outcome of refractive surgery or customized aberration correction. To clarify this issue, we asked whether these drug–induced changes arise from the cornea or from the crystalline lens. Methods: The 2nd generation Indiana corneal topographer/aberrometer was used to measure corneal and whole–eye aberrations [Zhou et. al. JOSA, in press]. Measurements were obtained on the left eyes of 6 subjects (average age 33.2 ± 10.6 years, excluding one presbyopic control eye) under three conditions: relaxed accommodation but no cycloplegic drug (ND), instillation of 2 drops 1% tropicamide (Trop), and instillation of 2 drops 1% cyclopentolate HCl (Cycl). For each condition, five repeated measurements with realignment between measurements were obtained on cornea and whole–eye respectively. Data analysis was for 5.5 mm pupil. Paired statistical tests of drug effects were based on univariate comparisons of individual Zernike coefficients, multivariate comparisons of a vector of coefficients, and RMS of the difference between reconstructed wavefronts obtained with and without drugs. Results: As expected of cycloplegic drugs, the primary effect of Trop and Cycl on whole eye aberrations was a small change in the negative direction (i.e. less myopia) of the defocus coefficient Z2\0. However, neither drug had a consistent effect on other Zernike coefficients. When the defocus coefficient was included in the spectrum of Zernike coefficients, statistical tests indicated that both drugs had a significant effect on the wavefront aberration of the whole eye for all subjects except the presbyope. When defocus was omitted from the analysis, only Trop had a significant effect on the Zernike spectrum and on the RMS of the difference wavefronts. This result was also obtained when only higher–order aberrations were analyzed. Neither drug affected the aberration structure of the cornea. With few exceptions, Trop and Cycl had no significant effect (p < 0.01) on individual Zernike coefficients for corneal aberrations from 2nd to 4th order. Conclusions: Neither Tropicamide nor cyclopentolate HCl affects corneal wavefront aberrations. Therefore, the consistent effects of these drugs on the whole eye’s state of focus and the inconsistent effects on other Zernike aberrations must be due to changes in the crystalline lens. These changes should be taken into account when planning refractive surgery and customized aberration correction.
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