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Jason D. Marsack, Konrad Pesudovs, Daniel C. Kist, Edwin J. Sarver, Raymond A. Applegate; Is the fit error associated with the Zernike polynomial in keratoconus visually important?. Journal of Vision 2004;4(11):66. doi: https://doi.org/10.1167/4.11.66.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Keratoconus is a corneal disease characterized by elevated visually debilitating aberrations, the bulk of which arise from an abnormal corneal first surface. Correction of aberrations with soft customized contact lenses could revolutionize keratoconus management. Zernike fitting in contact lens design is attractive because of known effects of rotation and translation of the lens relative to the eye.1 However, when a Zernike fit is made to a keratoconus wavefront, significant error in the fit can exist.
Purpose: To simulate the visual impact of keratoconus Zernike fit error on high contrast, photopic visual acuity.
Methods: Eight keratoconus corneal topographies were identified ranging in power from 44D to 78D in 5D steps. 4mm Zernike aberration coefficients through the tenth order and residual wavefront error were calculated. For the second to tenth order Zernike correction, nine PSFs (calculated from the remaining Zernike terms and the fit error) were convolved with high contrast logMAR letter charts and read by three normal observers under cycloplegia with aberrations minimized. Acuity was scored to the letter counting correct responses to the fifth miss.
Results: For eyes with less than 60D maximum corneal power, a 6th order Zernike fit was sufficient to provide acuity equivalent to that on an unaberrated chart. For the most aberrated eyes in the study (71D and 78D max power), acuity was diminished 0.1 logMAR for a 10th order Zernike correction.
Conclusion: It appears possible to use Zernike expansion representation of a keratoconus wavefront to correct high contrast, photopic acuity for all except the most severe keratoconus cases.
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