Extended wear contact lenses

The chapter shows how the successful design of polymers for contact lens applications depends on the need to provide a balance of properties appropriate to the ocular environment. The principal relevant aspects of the anterior eye are tear film, eyelid and cornea, which govern the requirements for surface properties, modulus and oxygen permeability, respectively. In the case of extended (overnight) wear, oxygen permeability is the most critical because of the reduced availability of oxygen to the avascular cornea. The relationship between permeability requirements and the developing view of the needs of the cornea, in terms of oxygen consumption, are discussed and the particular roles of fluorine and silicon in the design of successful polymers described. The evolution of polymer design is taken as a background for the consideration of the current generation of silicone hydrogels, which have proved to be the most successful family of materials for this demanding application. 2010 Woodhead Publishing Limited All rights reserved.