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Scott Curtin, Michelle Seitz, Meng Ouyang, Katarina Tomic, Meredith Wiseman, Hanny Vanwersch; Characterization of contact lenses through oxygen permeability, equilibrium water content, and silicone content. Invest. Ophthalmol. Vis. Sci. 2013;54(15):490.
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© ARVO (1962-2015); The Authors (2016-present)
In an effort to contribute to the growing knowledge base of materials properties of silicone hydrogel (“SiHy”) contact lenses and improve material design for formulation, DSM has evaluated three principal material parameters that affect oxygen permeability (Dk); amount of silicone component present, intrinsic permeability of silicone component, and connectivity of silicone-containing phase
The coulometric oxygen permeability (Dk) and equilibrium water content (EWC) of commercial SiHy contact lenses were measured at DSM using methods described in ISO 18369-4:2006 and ANSI Z80.20-2010. A modified Mocon MH 2/21 was used to measure the oxygen permeability for 5 contact lenses using CIBA Vision O2 Optix for the Q value. The silicon and fluorine contents of dried commercial lenses were measured by X-ray fluorescence to approximately ± 0.5 wt%.
CIBA Vision Air Optix 108±3.3 (110), CIBA Vision Dailies Total One 131±4.3 (140), Acuvue Oasys 105±1.6 (105), Acuvue Trueye 114±2.1 (110), Coopervision Biofinity 128±6.1(128) with manufacturer-claimed values in parentheses and all lenses besides CIBA Vision lenses were reported using polarographic method . A wet blot gravimetric method was used to measure EWC for six lenses with measured values closely matching reported values. CIBA Vision Air Optix 32.7±0.5% (33%), CIBA Vision Dailies Total One 29.9±0.8% (33%), Acuvue Oasys 37.3±0% (38%), Acuvue Trueye 44.5±0.4% (46%), Coopervision Biofinity 46.3±0.8% (48%), and CIBA Vision O2 Optix 30.5±0.5% (33%). Additionally, the atomic silicon and fluorine contents of the dried lenses were measured with X-ray Fluorescence.
Dk of SiHy lenses can be understood in terms of three principal material parameters: the amount of silicone component present, the intrinsic permeability of silicone component, and the connectivity of silicone-containing phase. The volume fraction of the silicone phase is a more meaningful parameter than EWC in understanding Dk and it can be estimated using the EWC and atomic percentages of Si and F. A simple morphologically based permeability model can describe the Dk of commercial lenses. This gives a framework for how to achieve sufficient Dk while minimizing use of silicone materials by optimizing connectivity and intrinsic permeability of silicone phase. ©2012 DSM. All rights reserved.
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