The change in internal aberrations following myopic corneal laser refractive surgery

Abstract

In virgin eyes, the internal aberrations compensate corneal aberrations, and it has been suggested that the compensation may be feedback-driven and developmental, with active or passive adaptive mechanisms potentially responsible for the aberration auto-compensation. The purpose of this study is to investigate the internal higher order aberrations (HOA) following laser in situ keratomileusis (LASIK). Prospective corneal and internal HOA were measured pre-operatively and 6 months post-operatively on 50 consecutive LASIK patients with the OPD-Scan. There were increases to corneal HOA terms Z⁰₄ (0.215 ± 0.092 μm to 0.381 ± 0.180 μm), Z⁰₆ (0.002 ± 0.018 μm to 0.049 ± 0.034 μm) and Z⁴₆ (0.010 ± 0.017 μm to 0.018 ± 0.016 μm) with corresponding increases to internal HOA terms Z⁰₄ (-0.176 ± 0.102 μm to -0.218 ± 0.121 μm), Z⁰₆ (0.004 ± 0.022 μm to -0.010 ± 0.036 μm) and Z⁴₆ (0.008 ± 0.106 μm to -0.015 ± 0.054 μm). The increases in internal aberrations attenuated the increase in corneal aberrations, providing an overall lower quantity of total aberration. A greater increase in corneal spherical aberration and associated compensation was found to occur with greater degrees of attempted myopic correction. Corneal spherical aberration and Z⁴₆increased with corresponding increases in the internal spherical aberration and Z⁴₆ following LASIK. This may be an active compensatory mechanism of the internal optics to change, in order to reduce the effect of induced corneal HOA.