Pressure phosphene tonometry versus Goldmann applanation tonometry for measuring intraocular pressure before and after LASIK

PURPOSE: To compare pressure phosphene tonometry with Goldmann applanation tonometry for measuring intraocular pressure (IOP) before and after LASIK. METHODS: Forty-three (18 men and 25 women) consecutive healthy patients underwent complete pre- and postoperative LASIK ophthalmologk: assessments including manifest and cycloptegic refraction, keratometry, and central corneal thickness. Three repetitive sets of pressure phosphene tonometry and Goldmann applanation tonometry measurements were performed the day before and 3 months following uneventful LASIK. RESULTS: Mean preoperative spherical equivalent refraction was -4.70±2.50 diopters (D) (range: -1.50 to -12.90 D) and mean preoperative keratometry was 43.95±1.08 D. After LASIK, spherical equivalent refraction was +0.23±0.11 D and mean keratometry was 39.46±2.28 D. Preoperative pressure phosphene tonometry (12.16±1.58 mmHg) and Goldmann applanation tonometry (12.01±1.55 mmHg) IOP measurements were similar. Postoperative IOP was 10.30±1.16 mmHg with Goldmann applanation tonometry and 12.20±1.62 mmHg with pressure phosphene tonometry. The postoperative IOP difference between Goldmann applanation tonometry and pressure phosphene tonometry was 0.15±1.12 mmHg (P=.41). The mean change in pachymetry after LASIK was 68.73±73 μm. The change in Goldmann applanation between preoperative and postoperative LASIK values was 1.71±1.43 mmHg (P<.0001), a change that was strongly correlated with changes in corneal thickness (R=0.75, P<.0001) and keratometry (R=0.72, P<.0001). No such correlations were found with pressure phosphene tonometry. CONCLUSIONS: Goldmann applanation tonometry-measured IOP decrease after LASIK is strongy correlated with a decrease in central corneal thickness and changes in keratometry, whereas pressure phosphene tonometry-measured IOP is independent of corneal thickness. Pressure phosphene tonometry appears to be a more reliable method for recording tonometry in these patients.