The influence of lens power and center thickness on the intraocular pressure measured through soft lenses: A comparison of two noncontact tonometers

Purpose: To quantify the influence of soft contact lens power and thickness on the intraocular pressure (IOP). Methods: Thirty-nine young, healthy adult volunteers completed this study. One eye of each subject was randomly assigned either a +6D or a -6D high water content daily disposable lens. The other eye was fitted with the second lens. Triplicate measurements of IOP were taken before, during, and after contact lens wear. Each time, IOP was assessed in a randomized order with two noncontact tonometers. The lenses were swapped between eyes during a second session of measurements, one week later. Results: In the first session with the +6D lenses, the average IOPs (+/- SDs) before, with the lenses fitted, and after the lenses were removed, were: 14.3 +/- 2.9 mmHg, 17.0 +/- 3.3 mmHg and 13.9 +/- 3.1 mmHg, respectively, for the CT80 and 13.6 +/- 3.1 mmHg, 17.1 +/- 4.5 mmHg and 13.3 +/- 2.9 mmHg, respectively, for the PT100. The corresponding values for the first session with the -6D lenses were: 14.3 +/- 3.1 mmHg, 13.1 +/- 3.1 mmHg and 14.1 +/- 3.3 mmHg, respectively, for the CT80 and 13.6 +/- 3.2 mmHg, 13.0 +/- 3.0 mmHg and 13.6 +/- 3.2 mmHg, respectively, for the PT100. IOP significantly (P<0.05) increased (+Delta IOP= 2.7 +/- 0.4 mmHg with the CT80 in the first session) with the +6D lenses, but decreased (P<0.05) when the -6D lenses were fitted (-Delta IOP = 0.6 +/- 0.2 mmHg with the PT100 in the first session). The soft contact lens-induced changes were consistent between sessions but varied between tonometers. Conclusions: The measurement of IOP through soft contact lenses resulted in consistent, statistically significant differences in IOP, which were not uniform across tonometers and which did not appear to be solely related to the central thickness of the soft contact lenses. (C) 2012 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.