Influence of the thermo-oxidative degradation on the chemical structure of contact lenses

In this work, four silicone-hydrogel contact lenses, Purevision® 2 (balafilcon A), Air Optix Aqua™ (lotrafilcon B), Acuvue® Oasys™ (senofilcon A) and Biofinity™ (comfilcon A), and one conventional lens, Acuvue® 2 (etafilcon A), were submitted during 5 weeks at a temperature of 37 °C under an air atmosphere. They were characterized initially and along exposure time in what concerns to the refractive index, water content, transmittance in the ultraviolet-visible region and chemical structure. From the results presented in this work it was possible to observe that in all lens the refractive index increases till 21 days and the water content decreased. At the end of the exposure these parameters are more variable depending on the lens studied. In what concerns to the transmittance in the ultraviolet-visible region it can be concluded that after exposure all lenses present a higher transmittance than initially. From this work it was possible to conclude that there were no significant changes in the wavenumbers where the main functional groups vibrate and in the intensity of the respective bands after 5 weeks of exposure.