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Jens Buehren, Kristina Otto, Xenia Weiner, Thomas Kohnen; Corneal Anterior, Posterior And Total Higher-order Aberrations And Their Implication For Optical Quality In Normal And Keratoconus Eyes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4185.
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To test the hypothesis that the posterior corneal surface compensates for the anterior corneal higher-order aberrations (HOA) and therefore improves the optical quality of the cornea.
From 97 normal eyes of 58 patients and 29 eyes of 21 patients with early to moderate keratoconus (KC) corneal topography scans were taken with a commercial Scheimpflug system (PentacamTM, Oculus, Germany). Wavefront aberrations from the anterior and posterior surface and the resulting wavefront aberrations of the total cornea were calculated using a Zernike decomposition up to the 8th order. The optical quality metric BCVSOTF (visual Strehl ratio based on the optical transfer function, simulated for best spectacle correction) was computed for a pupil diameter of 6 mm (VOL-Pro 7.14, Sarver and Ass.). Linear multiple regression analysis was applied to determine the influence of the difference in total and anterior corneal HOA on the difference in optical quality of the total cornea and corneal first surface (presumed compensation effect).
The BCVSOTF difference between the total cornea and the corneal first surface was 0.07 ±0.07 log units (-0.13 to 0.2) in normal eyes and 0.05 ±0.09 (-0.17 to 0.2) log units in KC eyes. In normal eyes, the VSOTF difference was influenced by the difference of coma RMS, spherical aberration RMS and the RMS of all other HOA (R²=0.46). In KC eyes, no significant influence of HOA difference on BCVSOTF difference could be found.
There is partial compensation of HOA of the first surface by those of the posterior surface in the majority of normal and KC eyes. However, in terms of optical quality this effect was marginal in most eyes.
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