Lysozyme lens deposits

Components of the tear attach to contact lenses by electrostatic and van der Waals forces and build up to form deposits. Deposits on the surface and in the lens matrix may result in reduced visual acuity, irritation, and in some instances serious ocular complications. The composition of deposits vary because of the complexity of an individual s ocular physiology-pathology. Lysozyme is a major component of soft lens deposits, especially found on high-water-content ionic lenses [312]. Calcium [313] and lipids [314] are infrequent components of deposits, occurring as inorganic salts, organic salts, or as an element of mixed deposits, or as a combination thereof [315,316]. 

The understanding and control of the interactions of proteins with solid surfaces is important in a number of areas in biology and medicine. In the last twenty years there has been considerable interest in protein interactions with materials used in medical devices (1-3). One area of particular interest to the contact lens industry is in the interaction of tear proteins with contact lenses. One of the major constituent of protein deposits on lenses is lysozyme. An understanding of human lysozyme interaction with contact lens materials is essential to the minimization and elimination of contact lens deposits. 

We have prepared an ATF solution using a protocol similar to those previously reported (7, 15). Our preparation contained three of the major proteins found in tears and lens deposits, namely, lysozyme, albumin and mucin. Hydrogels prepared from HEMA, monomers 1 or 2, or their mixed combinations were incubated in ATF for 24h at 36 °C, and the adsorbed proteins were quantified using the BCA assay (7). The results of the study are presented in Figure 2. 

Clinical experience has shown that certain types of lens materials are more prone to deposit problems. In general, lenses with negatively charged moieties at the surface accumulate greater amounts of lysozyme, the principal tear film protein (10). The introduction and use of disposable lenses make these deposits and their clinical problems less significant. 

Lens hazing and protein deposition are common problems for wearers of soft contact lenses. Previous experiments with hydrophobic-hydrophilic copolymers exposed to plasma showed protein adsorption to be minimal at intermediate copolymer compositions. Adsorption of proteins from artificial tear solutions to a series of polymers and copolymers ranging in composition from 100% poly (methyl methacrylate) (PMMA) to 100% poly(2-hydroxyethyl methacrylate) (PH EM A) was measured. The total protein adsorption due to the three major proteins in tear fluid (lysozyme, albumin, and immunoglobulins) was at a minimum value at copolymer compositions containing 50% or less PH EM A. The elution of the adsorbed proteins from these polymers and copolymers with various solutions also was investigated to assess the binding mechanism. 

There are other types of proteins that adhered to the CL surface such as albumin or lactoferrin, whose mechanism of adhesion seems to be different from lysozyme. However, because of the large molecular weight of albumin compared to lysozyme, this protein only forms deposits on the lens surface without penetration into the lens matrix [108]. Quantities of proteins recovered from worn CL are on the order of <50 pg per lens for non-ionic materials to more than 500 pg per lens for ionic group IV materials [101,109]. 

Previous in vitro studies have confirmed the cdfin-ity of certain deposits for certcun materials [102, 103]. Furthermore, ui in vivo study hcis shown that despite significant interaction between lens matericd cuid Ccffe system, the main contributor to the amount of cholesterol and lysozyme deposited on silicone hydrogel materials is lens material [112]. This effect was particularly remarkable for lotrafilcon B that deposited between 0.1 to 0.5 mg of cholesterol irrespective of the care system used. Polar and non-polar lipids show differences in their pattern of adhesion to different Si-Hy CL materials [103,113]. 

---