The accuracy of Goldmann applanation tonometry over silicone hydrogel contact lenses in patients with glaucoma

Purpose: To investigate the accuracy of measuring intraocular pressure over a silicone hydrogel contact lens using Goldmann applanation tonometry in eyes with glaucoma. Methods: This was a prospective, randomized study and enrolled 28 patients (28 right eyes) with primary open angle glaucoma. Intraocular pressure was taken with and without a silicone hydrogel contact lens (-0.50 D), in situ (using Goldmann applanation tonometry), in a randomized order of measurements. Statistical analysis was performed using paired t-test and Bland-Altman plot. Results: The mean difference (+/- standard deviation) found between intraocular pressure measurement without (mean 16.7 +/- 3.2 mmHg) and with (mean 17.3 +/- 3.0 mmHg) contact lens was found to be -0.57 +/- 2.3 mmHg (95% confidence interval, -1.5 to 0.3). No significant statistical difference was found between the two groups with paired t-test (p = 0.19). The Bland Altman plot showed some evidence of increasing variability of differences between two measures of intraocular pressure, with increasing intraocular pressure. The 95% limits of agreement of the Bland Altman plot were unacceptably large (-5 mmHg to 3.9 mmHg). Conclusion: Agreement between Goldmann applanation tonometry with and without contact lenses seems to be poor in patients with glaucoma, especially for high intraocular pressure. (C) 2014 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.