Effect of mild to moderate myopic correction by laser-assisted in situ keratomileusis on intraocular pressure measurements with Goldmann applanation tonometer, Tono-Pen, and pneumatonometer

Purpose: To evaluate the effect of mild to moderate myopic correction by laserassisted in situ keratomileusis (LASIK) on intraocular pressure (IOP) measurements with three tonometers: the Goldmann applanation tonometer, Tono-Pen, and pneumatonometer. Patients and Methods: In a prospective study of a clinic-based population undergoing elective LASIK surgery for myopia correction, IOP measurements were obtained preoperatively and postoperatively with a Goldmann applanation tonometer, Tono-Pen, and pneumatonometer. Central corneal thickness and keratometric and astigmatism measurements were also obtained before and after surgery. A paired t test was used to evaluate the significance of differences between preoperative and postoperative IOP measurements with each instrument. Linear regression was used to correlate IOP measurements with degree of myopia corrected, astigmatism, and central corneal thickness before and after surgery. Results: The study included 66 eyes of 34 individuals with a mean preoperative refractive error of -5.66 + 2.3 D (mean + SD). The reduction of central corneal thickness after LASIK of 0.032 + 0.030 mm (mean + SD) was statistically significant (P < 0.0001). However, there was no statistically significant change in mean IOP after the procedure with the Goldmann applanation tonometer or the Tono-Pen, while the pneumatonometer, was associated with a small but statistically significant decrease in mean IOP of 1.1 mm Hg. Conclusion: In this group of patients with mild to moderate myopia, LASIK had little or no statistically significant influence on IOP readings obtained with a Goldmann applanation tonometer, Tono-Pen, or pneumatonometer. This finding is in contrast to earlier reports of greater amounts of myopic correction, in which significant reductions in measured IOP were observed. Further study is needed to determine whether a critical amount of corneal change after LASIK is required to have a significant effect on IOP measurements.