Studies of the Ocular Compatibility of Hydrogels. White Spot Deposits--chemical Composition and Geological Arrangement of Components

Light, SEM and histochemical techniques were used to determine the architecture and composition of elevated deposits on a variety of commercial lenses of differing bulk and surface chemistries and wear protocols. Spoilt lenses were derived from controlled lens wear trials and additional clinical sources. Elevated deposits display a complex multilayered structure, unaffected by variations in wear protocol or bulk and surface chemistries. These deposits are predominantly composed of tear-derived lipids laid down in a well-defined fashion. The primary layer is composed of unsaturated lipids, whilst the secondary and tertiary layers are dominated by cholesterol and cholesterol esters. The composition and location of deposit components is unaffected by variations in, wear protocol, chemistry of the lens matrix, or tear composition of lens wearers. These findings suggest that unsaturated lipids are responsible for the biological interfacial conversion of hydrogel lenses, reducing their compatibility with the ocular environment.