The plasma treatment of contact lenses
This thesis investigates the use of low temperature plasmas as a means of improving the surface properties of hard gas permeable contact lenses. It is important that the polymers used for this application should have good optical properties, should allow transport of oxygen to the cornea and be biocompatible, that is they should not stimulate an adverse response in the tissues which they contact. Whilst most patients have no problems with current materials there are a significant number who experience irritation of the eyes and abnormal build up of deposits on the lens surface. It has been found that mild oxygen plasma treatment of the contact lens can be helpful in alleviating these problems. In this volume the effects of such treatment are examined by x-ray photoelectron spectroscopy and alternative treatments proposed. It is found that the oxygen plasma treatment increases the wettability of the lens surface by the incorporation of oxygen in the polymer. This effect decays with time but is not wholly lost on prolonged storage. The mechanism of this decay appears to be a migration of oxidized material from the surface and is dependent on the storage conditions. During this decay an anomalous transient increase in hydrophilicity was encountered which can be associated with the temporary return of highly oxidized material to the surface. This effect is observed in other polymers and can be shown to be temperature dependent. The use of plasma polymerization as an alternative treatment was investigated and a number of materials produced with similar surface properties to the oxygen treated lens material. It was hoped that a coating would be generally applicable to a variety of lens materials.*Adsorption studies showed that the oxygen treated material has the property of reversibly adsorbing glycoproteins which may account for its performance in the eye. Some of the plasma polymer coatings gave a similar response.