Purpose: To investigate ocular Higher Order Aberrations (HOA) by examining Zernike polynomials with a novel application of clustering analysis adjusted for age, refractive error and pupil size.Methods: Wavefront aberrations were measured with wavefront aberrometry (ZyWave, Technolas Perfect Vision) on 1509 patients (57.9% females) with a mean age of 43.1 ± 12.0 years (range 18 to 71). We modeled the association of 15 pupil size adjusted (PSA) Zernike polynomials (3 rd to 5 th order) with age and refractive error using linear regression. A statistical method called clustering of linear models (CLM) was used to identify the clusters of Zernike polynomials.Results: Fifteen Zernike polynomials were grouped into four clusters through CLM adjusting for age and refractive error. In the first cluster (Z 311 , Z 310 , Z 331 and Z 330 ), the PSA Zernike polynomials increased with refractive error (regression coefficient, 0.0041; 95% empirical confidence interval [CI]: 0.00015 to 0.0081) but significantly decreased with age (coefficient, -0.0021; 95% CI: -0.0031to-0.0010). In the second cluster (Z 400 ), the PSA Zernike polynomials decreased with refractive error (coefficient, -0.0065; 95% CI: -0.010 to -0.0029) but increased with age (coefficient, 0.004; 95% CI: 0.0031 to 0.0049). No significant associations were detected in the remaining two clusters (secondary astigmatism and secondary coma).
Conclusion:Taking advantages of regression model that accounts for pupil size, these results provide a better understanding of HOA in a more population-based perspective. Our clustering approach has the functional capacity to predict the values of Zernike polynomials that are relevant for clinical and commercial use.
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IntroductionHigher Order Aberrations (HOA) is distortions in light that result from physical alterations of the optical pathway. The primary ocular factors that contribute to HOA are the tear film, cornea and lens. Wavefront assessment instruments such as the Hartmann-Shack Sensor provide data from which the aberrations of the human's eye are estimated. The understanding of HOA as applied to the visual system and the commercialization of devices that measure HOA has greatly expanded the use of these methods in the clinical setting. Zernike polynomials have been commonly used as the standard method for describing the shape of an aberrated wavefront [1].Zernike polynomials are an orthogonal series of basic functions normalized over a unit circle. They provide a precise mathematical model that has the ability to capture global shape.An important characteristic of Zernike polynomials is that lower order polynomials approximate the overall features of the anatomic shape of the eye very well, while the higher ordered polynomial terms capture local surface features only. A second important property of Zernike polynomials is that they have a direct relationship to optical function. These optical and geometric properties make Zernike polynomials particularly useful for study of the cornea and the optical syste...