Tonometry after laser in situ keratomileusis treatment

Purpose: To assess the reliability of intraocular pressure measurements by Goldmann applanation tonometry versus pneumotonometry after laser in situ k eratomileusis for myopia. Patients and Methods: In this prospective study, corneal Goldmann applanati on tonometry and pneumotonometry measurements were made in 118 eyes of 60 p atients before and 1 and 3 months after undergoing laser in situ keratomile usis for myopia. Manifest refraction, ultrasonic corneal thickness measurem ents, and keratometry readings were also obtained. Results: Preoperative intraocular pressure showed a good correlation betwee n Goldmann applanation tonometry and pneumotonometry values (Pearson r = 0. 71; P < 0.001). although Goldmann applanation tonometry readings were sligh tly higher at low intraocular pressure values and slightly lower at high in traocular pressure values. After a mean stromal ablation depth of 77.1 mum. mean intraocular pressure by Goldmann applanation tonometry decreased sign ificantly (P < 0.001) from a preoperative value of 14.8 +/- 11.9 mm Hg to 1 1.9 +/- 2.1 mm Hg and 11.7 +/- 1.7 mm Hg after 1 and 3 months, respectively . Mean pre- and post-laser in situ keratomileusis measurements by pneumoton ometry were similar (P = 0.8). Differences of postoperative intraocular pre ssure measurements by Goldmann applanation tonometry and pneumotonometry we re statistically significant. After 3 months, there was a poor correlation between Goldmann applanation tonometry and pneumotonometry intraocular pres sure values (Pearson r = 0.58). Postoperative intraocular pressure decrease in applanation tonometry correlated with changes in keratometry, spherical equivalent, and central corneal thickness. Regression analysis showed a de crease of 2.9 mm Hg per 70 mum reduction in central corneal thickness. Conclusions: Contact pneumotonometry measures the IOP reliably after laser in situ keratomileusis for myopia, whereas Goldmann applanation tonometry u nderestimates the intraocular pressure. This may be important in the treatm ent of any future glaucoma.