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.