The ex vivo wettability of soft contact lenses

Purpose. To investigate the ex vivo wettability of Etafilcon A contact lens es over an eight hour period of wear and observe the influence of surfactan t pre-treatment. Methods. Etafilcon A hydrogel lenses, comprising poly[2-hydroxyethyl methac rylate-co-methacrylic acid] and 58% water, were soaked for 12 hours in eith er 0.9% saline (control) or a 1% aqueous solution of poloxamine 1107 (treat ed). The advancing and receding contact angles were subsequently determined ex vivo after various periods of wear in six adapted contact lens wearers using a single-blind, randomised protocol. Contact angles were measured wit h a dynamic contact angle tensiometer, using the Wilhelmy plate technique. Patient comfort scores were recorded and the static surface tensions of the probe fluids assessed. Results. Control lenses exhibited no change in wetting angles over time, in dicating a lack of surface modification by components within the tear film. Treated lenses exhibited a significantly reduced advancing angle (p<0.001) and hysteresis angle (p<0.001) when compared with control lenses. In addit ion, treated lenses were consistently rated as being more comfortable than control lenses (p=0.04). Conclusions. This study has shown clearly that new Etafilcon A lenses do no t exhibit significant changes in wettability during the initial four hour w earing period. Pre-treatment of such lenses with a polymeric surfactant res ults in wetting of the lenses due to the adsorption of surfactant. The surf actant is retained by the lens for at least eight hours of wear, resulting in significant improvements in subjective comfort, especially over the firs t 30 minutes of wear.