LASIK-induced aberrations: comparing corneal and whole-eye measurements

Abstract

Purpose: To compare the change in aberrations produced by laser-assisted in situ keratomileusis (LASIK) measured by either front surface corneal aberrometry or Hartmann-Shack whole-eye aberrometry.

Methods: This was a retrospective case series from consecutive patients treated with LASIK at the London Vision Clinic, London, UK. Corneal and ocular wavefront data were collected before and after LASIK for myopia and hyperopia. To control for centration of corneal and whole-eye aberration measurements, only patients with pupil offset (measured as the distance between the corneal vertex and the entrance pupil center) of 0.25 mm or less were recruited. Corneal front surface wavefront was obtained from a Placido-based corneal topography system (Atlas), and whole-eye wavefront was measured by Hartmann-Shack aberrometry (WASCA) before and at least 3 months after surgery. All aberrations were calculated up to the fourth order for the 6-mm pupil diameter. Change in HORMS (higher-order root mean square [RMS]) and all individual Zernike coefficients from the second to the fourth order were compared.

Results: One hundred myopic eyes and 50 hyperopic eyes were included for analysis. For myopic LASIK, the change measured by corneal aberrometry or whole-eye aberrometry differed on average by 0.077 μm for HORMS, by 0.024 μm for secondary astigmatism, and by 0.065 μm for spherical aberration (p ≤ 0.003). For hyperopic LASIK, there was no statistically significant difference between the change measured by corneal aberrometry and whole-eye aberrometry for third- and fourth-order individual Zernike coefficients (p ≥ 0.034). However, the change in HORMS measured by whole-eye aberrometry was 0.095 μm greater than that measured by corneal aberrometry (p < 0.001).

Conclusions: This study demonstrated that when measuring the change in higher-order aberrations induced by LASIK, corneal front surface aberrometry measurement was not interchangeable with whole-eye ocular aberrometry.