Techniques for eliciting the identity and amount of deposits on soft contact lenses have improved consistently; however, there remain many questions regarding the role of specific deposit components in causing ocular reactions. We review the large body of literature on soft lens deposition to define the link between deposits and symptoms.
Our critique attempts to clarify areas of doubt in previous methodologies for analyzing deposits, and to focus on the aspects of deposition as relevant to inducing ocular responses. The principal features confounding previous experimentation are: variables in experimental design; methodological flaws, such as imperfect extraction of material from a lens; focus on determining the quantity of a component at the expense of considering its nature and biological activity; reporting of results from nonrepresentative wearing conditions and lenses.
Despite the introduction of disposable lenses, lens surface build-up remains an important factor in determining lens-wear success. The composition of deposits has been the target of many studies that show that lysozyme is the principal soilant on the lens surface. Estimates of protein quantities found on lenses are subject to the extraction technique but provide the common finding that Group IV lenses attract the greatest level of deposit. Nonionic lens surfaces have a greater affinity for lipids. The extent to which other species such as carbohydrates and minerals, contribute to lens deposits is less well defined. There are some clues to the structural basis for deposit formation, but further research is necessary to isolate the key events leading to deposits.
The sheer weight of energy that has been invested into examining lens coatings suggests that surface build-up plays a role in contact lens complications, although proof linking a specific component with a specific biocompatibility issue remains lacking. Emphasis should be placed on determining the nature, as well as quantity, of lens deposit components and on the development of clinical methods that can link symptomatology with derived deposit patterns.
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