Alterations in intraocular pressure and the CorVis parameters after LASIK

Abstract

The reduction of corneal thickness following laser-assisted in-situ keratomileusis (LASIK) requires a correction of intraocular pressure (IOP) measurements. The corneal visualization Scheimpflug technology (CorVis ST, Oculus, Wetzlar, Germany) not only measures the IOP and central corneal thickness (CCT) but also determines 10 additional corneal parameters, such as the time to first and second applanation and velocity. Besides CCT we compared various corneal parameters before and after LASIK in order to detect possible correlations and to correct IOP measurements. Measurements with CorVis ST were made before and after LASIK in 45 myopic patients (45 left eyes). We compared the IOP and CorVis ST parameters using a paired t‑test before and after LASIK and corrected for possible correlations in a multifactorial linear model. Finally, we correlated the changes in IOP to changes in biomechanical parameters. We observed a direct correlation between the IOP measurements and the corneal thickness. The IOP was underestimated by 0.039mmHg per micrometer in reduction of corneal thickness. The multifactorial linear model showed a correlation of IOP change to A2 velocity and the radius of applanation. Surgical thinning of the central cornea via LASIK demonstrated a direct correlation between corneal thickness and IOP measurements using the CorVis ST technique. Postoperative changes of the A2 velocity and the applanation radius also had a statistically significant influence on post-LASIK IOP measurements. Our findings could be useful to obtain more precise post-LASIK IOP measurements.