Evaluation of the effect of contact lens use on intraocular pressure measurement

Purpose: The aim of this study was to investigate the accuracy and reliability of intraocular pressure (IOP) measurements performed over contact lenses using a pneumotonometer, TonoPen, and rebound tonometer. Materials and Methods: The study included 60 healthy patients who presented to the Contact Lens Clinic of the Ophthalmology Department at Manisa Celal Bayar University Hafsa Sultan Hospital. Following a comprehensive ophthalmologic examination, contact lens measurements providing the best visual acuity and spherical equivalent measurements were recorded. Based on the patients' refractive errors, spherical and toric contact lenses made from samfilcon A silicone hydrogel material were used. Central corneal thickness and keratometry measurements were obtained using a Scheimpflug camera. IOP was measured in all patients without contact lenses using GAT (Goldmann Applanation Tonometry), pneumotonometer, TonoPen, and rebound tonometer. Then, IOP measurements were repeated over contact lenses using the pneumotonometer, TonoPen, and rebound tonometer, and the results were recorded. Each device's two sets of measurements were compared separately. The difference between the measurements was analyzed in relation to GAT values, spherical equivalent, central corneal thickness, and keratometry measurements. Results: The mean IOP measured with GAT was 13.68 ± 2.31 mmHg. The mean IOP measured with the pneumotonometer was 14.53 ± 2.61 mmHg without contact lenses and 13.73 ± 2.48 mmHg over contact lenses. Measurements over contact lenses were found to be significantly lower(p<0.05). The mean IOP measured with the TonoPen was 14.99 ± 2.60 mmHg without contact lenses and 14.24 ± 2.36 mmHg over contact lenses, which was also significantly lower(p<0.05). The mean IOP measured with the rebound tonometer was 14.30 ± 2.84 mmHg without contact lenses and 15.29 ± 2.84 mmHg over contact lenses. The measurement differences was found to be statistically significant(p<0.001). The average differences between the two measurements were -0.80 ± 2.03 mmHg for the pneumotonometer, -0.75 ± 1.75 mmHg for the TonoPen, and 1.00 ± 1.70 mmHg for the rebound tonometer. No significant correlation was found between the measurement differences and spherical equivalent, central corneal thickness, or keratometry values. Conclusion: IOP measurements performed over contact lenses tend to be lower with the pneumotonometer and TonoPen, while higher with the rebound tonometer. However, these differences may not clinically significant. Keywords: intraocular pressure, contact lens, tonometer