Effect of Contact Lenses on Measurements by Non-Contact tonometry, Dynamic Contour Tonometry, and Tono-Pen

Purpose: To investigate the effect of soft contact lens wear on intraocular pressure (IOP) measurements obtained using non-contact tonometry (NCT), Pascal dynamic contour tonometry (Pascal-DCT), and the Tono-Pen. Methods: Twenty-nine eyes of 29 healthy volunteers were included in the study. Following a routine ophthalmologic examination, central corneal thickness was measured using an ultrasonic pachymeter. Intraocular pressure (IOP) was measured before and after soft contact lens application using NCT, Pascal-DCT, and the Tono-Pen in random order. The differences between pre- and post–soft contact lens measurements were statistically analyzed using the paired t-test. Results: The mean age of the 29 healthy volunteers who participated in the study was 52.6 ± 15.4 years (range, 21–73 years). Corneal thickness measurements in all participants ranged from 506 µm to 610 µm (mean, 557.4 ± 31.6 µm). Before soft contact lens application, mean intraocular pressure (IOP) values obtained with Goldmann applanation tonometry (GAT), NCT, Pascal-DCT, and Tono-Pen were 16.1 ± 2.8 mmHg, 16.7 ± 3.8 mmHg, 17.7 ± 2.6 mmHg, and 17.2 ± 3.6 mmHg, respectively (P = 0.6). After soft contact lens application, IOP values measured with NCT, Pascal-DCT, and Tono-Pen were 14.4 ± 3.8 mmHg, 16.5 ± 2.8 mmHg, and 16.9 ± 3.8 mmHg, respectively. IOP values measured with NCT and Pascal-DCT were found to be significantly lower after lens application (P < 0.01 for both). Although IOP values measured with the Tono-Pen were also lower after lens application, the difference was not statistically significant (P = 0.33). Conclusion: In this study, we demonstrated that IOP can be reliably measured using the NCT, Tono-Pen, and Pascal-DCT in a limited number of participants. However, it should be kept in mind that lower IOP values are obtained when measurements are performed with the NCT and Pascal-DCT without removing the soft contact lens. Although the Tono-Pen also yields slightly lower readings in eyes wearing a soft contact lens, it should be noted that the Tono-Pen appears to be the most accurate device for measuring IOP without lens removal.