A clinical comparison of the Xpert non-contact tonometer with the Goldmann applanation tonometer after penetrating keratoplasty

Purpose: To assess the agreement between the Xpert non-contact tonometer (NCT) and the Goldmann applanation tonometer in patients who have undergone penetrating keratoplasty, Methods: The study material consisted of 42 consecutive patients (43 eyes) who had undergone penetrating keratoplasty within the previous 13 months. Results: The slope of the linear relationship between the two measurement methods did not differ significantly from 1.0. The mean difference between the methods of 0.96 mmHg was not statistically significant. The range of intraindividual differences between the methods was from -9.8 to 22.8 mmHg. The standard deviation of differences was 6.62 mmHg. The 95% limits of agreement were -12.00 to 13.94 mmHg. There was no significant correlation between the central corneal thickness, astigmatism or transplant size and the difference between the methods. Conclusion: The Xpert NCT shows considerable variation from the Goldmann values. The degree of agreement with the true IOP value remains to be shown.