Dynamic contour tonometry (DCT) over a thin daily disposable hydrogel contact lens
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Dynamic Contour Tonometry (DCT) has been shown to measure the intraocular pressure (IOP) independent of corneal physical properties such as thickness, curvature and rigidity. The aim of this study was to find out if DCT remains accurate when it is applied on regularly shaped corneas while a thin, daily hydrogel contact lens (CL) is worn. Methods: This was a prospective, randomised study and included 46 patients (46 right eyes): 26 females and 20 males. The age varied from 22 to 66 years (mean: 43.0±12.70 years). IOP and ocular pulse amplitude (OPA) measurements were taken with and without a daily disposable hydrogel CL (−0.50 D), Filcon IV) in situ (using the DCT), with a randomised order of measurements. Results: The average value for the IOP measurements without CL was 16.51±3.20mmHg, and with CL in situ it was 16.10±3.10mmHg. The mean difference was 0.41mmHg and not found to be statistically significant (p = 0.074). The average value for the OPA measurement without CL was 2.20±0.79mmHg. With CL in situ it was 2.08±0.81mmHg. This gave a mean difference of 0.11mmHg and was statistically significant (p = 0.025). The Bland–Altman plot showed a maximum difference in IOP of +2.44 and −2.00mmHg (CI 0.95). Regarding OPA, the maximum difference was +0.81 and −0.60mmHg (CI 0.95). Conclusion: The presence of a thin hydrogel CL did not affect the accuracy of IOP measurements using the DCT. The ocular pulse amplitude was measured on average 5.45% lower with a CL in situ.