a resin is provided comprising a mixture of at least two polymerizable components , at least one photochromic additive , at least one additive and at least one polymerization initiator . the mixture of at least two polymerizable components is preferably selected from monofunctional , difunctional and multifunctional acrylates and methacrylates . the photochromic additive is preferably selected from spirooxazine additives and spiropyran additives . and the additive is preferably selected from antioxidants , radical scavengers and ultraviolet absorbers .