Additives and extras

It is normal practice for us to describe spectacle frame materials in terms of the principal materials present, and sometimes even to consider the coatings and minor components. However, there are many additives and raw materials which are never revealed to us by our suppliers. Awareness of many of these has surfaced because of skin reactions to spectacle frames which have gone as far as hospital evaluation and have been reported in the dermatological literature, rather than because the industry has been willing to reveal its secrets.
Reading such literature it soon becomes apparent that some of the older diagnoses  are questionable, as the combinations of materials seem a little unlikely. Analysis procedures are even now seldom reported other than patch testing with suspected substances. As many of the reactions may be rare and dermatological resources are limited, it is likely that reporting depends very much on luck and the majority of cases may go unreported. Every practitioner knows that if spectacles are the only problem item, the simplest and least traumatic advice for all concerned is simply to change the principal material from which the frame is made and hope that removes the causative agent. In the absence of published 'lists of ingredients' for spectacle frames akin to that now required for many other products and the current low profile of the Medicines and Healthcare Product Regulatory Agency (MHPRA) (formerly the Medical Devices Agency) in relation to optical devices, it is all that we can do.
Unlike the materials in the earlier A-Z series, there are no 'popular beliefs' about these substances to pass comment upon, as they are largely unknown within the optical community. Surprisingly, there only appear to have been two significant literature reviews of the area published. The most extensive was by Smith and Calnan in 1966,1 which is obviously now somewhat dated. A more recent, but limited, review was that of Nakada and Maibach (1998).2 Here we will look at where these substances might be found - where this information is available - and try to put them in a more general context than that of just spectacles.