Evaluation of intraocular pressure change after laser in situ keratomileusis using the pressure phosphene tonometer

Purpose: To evaluate the applicability of pressure phosphene tonometry in measuring intraocular pressure (IOP) after laser in situ keratomileusis (LASIK). Setting: Baptist Eye Clinic, Kyoto, Japan. Methods: Thirty-six eyes of 22 consecutive patients who had had LASIK for myopia were enrolled in this prospective comparative study. The mean age of the patients was 32.6 years +/-9.0 (SD). The IOP was measured using the pressure phosphene tonometer (FPT), Goldmann applanation tonometry (GAT), and noncontact tonometry (NCT). The patients themselves took measurements with the FPT before and 1 week after surgery. One-way analysis of variance followed by a Bonferroni/Dunn multiple comparison post hoc test was administered to compare the preoperative and postoperative measurements with each tonometer. These data were represented graphically using a method described by Bland and Altman. The relationship between each tonometric change and the central corneal thickness (CCT) or keratometry (K) changes after LASIK were evaluated with by Pearson correlation coefficient. Results: Statistically significant differences were found between preoperative and postoperative measurements with GAT and NCT but not with FPT. Preoperative and postoperative FPT readings conformed to the British Standard for reproducibility of a standard test method for IOP estimation. No significant correlation between FPT changes and CCT or K changes was found. Conclusions: Pressure phosphene tonometry measures IOP through the upper eyelid, and changes in corneal shape do not appear to have an effect on the IOP. The IOP measurements with FPT were constant before and after LASIK.