Comparison of intraocular pressure measurement results with different tonometers in patients with mucopolysaccharidosis

This study was aimed to compare non-invasive and potentially better tolerated tonometers such as Icare rebound tonometer and non-contact tonometer with Goldmann applanation tonometer, which is more difficult to tolerate, takes longer to measure and is the gold standard method because of skeletal disorders and mental retardation in patients with mucopolysaccharidosis. Intraocular pressure measurements were obtained with noncontact tonometer, Icare rebound tonometer and Goldmann applanation tonometer from 54 eyes of 54 patients who were followed up in the Glaucoma Unit of our Ophthalmology Department. Central corneal thickness was measured. A detailed anterior segment and fundus examination was performed and corneal clouding degrees and cup/disc ratios were noted. Icare rebound tonometer and non-contact tonometer measurements were compared with the gold standard Goldmann applanation tonometer measurements. The correlations of the results of these three tonometric methods with the central corneal thickness and corneal clouding degree were analyzed. Spearman correlation test, Wilcoxon signed rank test and Bland-Altman analysis were used for statistical analysis. When the mean intraocular pressures were compared, the mean intraocular pressures measured by non-contact tonometry and Icare rebound tonometry were statistically significantly higher than those measured by Goldmann applanation tonometry (Wilcoxon signed rank test; p<0.001 for Icare rebound tonometry and Goldmann applanation tonometry, p<0.001 for non-contact tonometry and Goldmann applanation tonometry). Spearman correlation analysis was used to analyze the correlations between intraocular pressure measurements. There was a high positive correlation between Icare rebound tonometry and Goldmann applanation tonometry (r=0.99, p=0.000) and between non-contact tonometry and Goldmann applanation tonometry (r=0.98, p=0.000). Bland-Altman analysis was used to evaluate the consistency of Icare rebound tonometry and non-contact tonometry with Goldmann applanation tonometry. The mean difference between Goldmann applanation tonometry IX and Icare rebound tonometry was -0.63 mmHg with a standard deviation of 0.71 mmHg and a 95% confidence interval of -2.02 to +0.76 mmHg and the mean difference between Goldmann applanation tonometry and non-contact tonometry was -1.17 mmHg with a standard deviation of 1.02 mmHg and a 95% confidence interval of -3.17 to +0.84 mmHg. When the correlation between the mean intraocular pressure measurements and central corneal thickness was evaluated, statistically significant high positive correlations were found between Goldmann applanation tonometry and central corneal thickness (r=0.72 p=0.000), between non-contact tonometry and central corneal thickness (r=0.74 p=0.000), and between Icare rebound tonometry and central corneal thickness (r=0.76 p=0.000). The relationship between the degree of corneal clouding and intraocular pressures measured by three tonometric methods was analyzed by Spearman correlation analysis. The correlation between the degree of corneal clouding and Goldmann applanation tonometer measurements was r=0.78, p<0.001, the correlation between noncontact tonometer measurements and the degree of corneal clouding was r=0.79, p<0.001, and the correlation between Icare rebound tonometer measurements and the degree of corneal clouding was r=0.80, p<0.001. There was a statistically significant high positive correlation between the degree of corneal clouding and intraocular pressure measured by three tonometric methods. In conclusion, all three tonometric methods are both correlated and consistent with each other. The results of the measurements made with the three tonometric methods are affected by the central corneal thickness. Icare rebound tonometer and non-contact tonometer have higher measurements than Goldmann applanation tonometer. The intraocular pressure measurement difference is greater with the non-contact tonometer than with the Icare rebound tonometer. The correlation and consistency between the three measurement methods show us that it is more accurate to use the same tonometric method in the follow-up of each patient individually. It also shows that Icare rebound tonometry or non-contact tonometry can be used instead of Goldmann applanation tonometry, which is the gold standard, in patients with mucopolysaccharidosis group who have compliance problems with measurement methods.