Analysis of contact lens deposits

Abstract

The most frequent cause of irritation from contact lenses is the formation of deposits from the tear film during lens wear. If such deposits are not removed by thorough daily cleaning, not only do they impair the optical quality of the lenses, their wettability and possibly their oxygen permeability, they may also cause chemic0-toxic o r as in the case of p ro te ins allergic reactions accompanied by the well-known symptom of protein conjunctivitis. In addition, such deposits generally provide a good medium for microorganisms, so infections are a further possible consequence. It is therefore of great importance that the contact lens practitioner should examine lenses that have become intolerable for possible deposits with a view to establishing the cause of the irritation. The question of course arises as to what use it is to find out what a deposit consists of. The answer is that in many cases the causes of irritation can be eliminated if we can determine the nature of the deposit and identify its origin. Iwould like to report on a number of tests which we have carded out on contaminated soft lenses and to explain a few of the methods we use to identify such deposits. The problem is not so much the nature of the deposit itself we know the approximate composition of the tear film and therefore have a specific basis for looking for particular chemical groups. The problem is rather that the quantities of deposits to be found on contact lenses are very small and often beyond the identification limits of conventional chemical techniques. We are in fact dealing with orders of magnitude ranging down to a tenth of a microgram (10-~g). This makes positive identification difficult and requires the use of special equipment. I am now going to discuss three different analytical procedures: Thin layer chromatography Scanning electron microscopy Light microscopy