The Effects of the Modulus of the Lens Material on Intraocular Pressure Measurement through Soft Contact Lenses

Abstract

Objectives: To investigate the effects of the modulus of the lens material on the intraocular pressure measurement using the Tono-Pen XL applanation tonometer through soft contact lenses. Method: Thirty eyes of 15 patients with myopia were evaluated. Intraocular pressure (IOP) measurements were performed using Tono-Pen XL directly over cornea, and subsequently through three soft contact lenses made up of different lens materials. All were -3.00 diopter soft contact lenses: lotrafilcon A with a low water content (24 %) and high modulus (1.4 MPa) (CL-I), balafilcon A with a moderate water content (36 %) and moderate modulus (1.1 MPa) (CL-II), and vifilcon A with a moderate water content (55 %) and low modulus (0.79 MPa) (CL-III). IOP measurements through contact lenses were compared with each other, and with direct corneal measurements. Results: The mean age of the patients (11 males and 4 females) was 26.86 ± 5.62 years. All measurements obtained through CLs were significantly higher than the direct corneal measurements. The measurements through CLs differed by 4.61 ± 0.54 mmHg (P = 0,001), 2.9 ± 0.46 mmHg (P = 0.001), and 1.94 ± 0.51 mmHg (P = 0,003) for CL-I, CL-II and CL-III, respectively. In the paired comparisons of measurements through CLs, all comparisons were significant except the comparison of measurements through CL-II and CL-III (P = 0.128). Conclusion: IOP measurements through silicone-hydrogel contact lenses with a high modulus and low water content were higher compared to the other contact lenses. While measuring IOP through CLs, the clinicians should consider the effect of the lens material and the features of the device used. © 2012 Royal Academy of Medicine in Ireland.