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]. 

Amiodarone-induced lens opacities have also been reported. Fine anterior subscapular lens deposits occur in approximately 50% of patients taking amiodarone in moderate to high dosages (600 to 800 mg daily) after 6 to 18 months of treatment.The deposits first appear as small golden brown or white-yellow punctate opacities located just below the anterior lens capsule. Unlike the lenticular deposits associated with chlorproma2ine therapy, which develop before corneal changes, the lens opacities... 

Giant papillary conjuctivitis may be caused by an immunologic response to the lens deposits (2). Lens cleaning procedures, especially heat disinfection, may denature proteins, while shear forces created by the eyelids moving over the lens may also contribute to further denaturation and subsequent... 

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. 

Protein deposition on materials surface is dependent on chemical nature of the surface (hydrophilicity, hydrophobicity, charge density) and also on the size and chemical composition of the proteins exposed to the synthetic surface (2). Since different biological media are composed of rather different types of proteins, materials designed for specific in lant applications must be tested using those proteins most likely encoimtered in vivo. Materials used in contact leiis applications are generally tested for in vitro protein adsorption using an artificial tear fluid (ATF) containing mixtures of proteins and lipids that are commonly found in hximan tear fluid and in contact lens deposits (15, 16). A... 

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. 

Poland s deposits tend to be located primarily in the west as isolated, lens-shaped deposits. There are other deposits in the center of the country at Turow, Konin /Goslawice/Patnow, Turek/Adomow, and Rogo2no. The production is used in power plants. 

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. 

Although a variety of test methods, eg, Dk, modulus, and tear strength, exist to determine key properties of potential contact lens materials, a number of properties, eg, wettabihty and deposition, have no predictive methodology short of actual clinical experience. 

There is great interest in developing soft lens materids that have high oxygen permeabdity and good wettabdity. Such lenses will provide patients with good comfort, high deposit resistance, and superior corneal health, particularly for extended wear appHcations. 

The principal problems for sdicone mbber as a viable lens material are the nonpolar nature, which gives Hpid deposits and wettabdity problems and the tendency to adhere to the cornea. Efforts to modify the sdicone lens surface for improved wettabdity have achieved limited success. These efforts include grafting hydrophilic monomers, such as HEMA, GM (150), and NVP (151—153), to the lens surface and plasma treatments of finished lenses. Efforts to improve the movement of sdicone lenses on the cornea with various lens designs have not been successfld, and the cause of lens—cornea adherence, which is not an exclusive problem of sdicone lenses, is an active area of research. 

A good example of a surface-modified lens is the Sola/Bames-Hind Hydrocurve Flite lens, introduced in 1986. The material for the commercial Hydrocurve lens, bufilcon A [56030-52-5] contains methacrylic acid and has a high affinity for protein and subsequent deposition. The surface of the Flite lens was chemically modified with the addition of diazomethane (190) to reduce the surface charge. In vitro testing demonstrated a decrease in protein adsorption (191). 

Quarz-keil, m. (Optica) quartz wedge, -kiesel, m. quartz gravel, -kristall, m. quartz crystal, rock crystal. -lager, n. quartz deposit, -linse, /. quartz lens, -mehl, -pulver, n. quartz powder- -rohr, n., -rohre, /. quartz tube, -sand, m. quartz sand, -scheibe, /. 

R. N. Diyashev, F. M. Sattarova, K. G. Mazitov, V. M. Khusainov, F. N. Mannanov, I. R. Diyashev, and V. A. Burtov. Extraction of oil from lens-shaped deposits—involves cyclic and portion-wise pumping-in of solutions of potassium carbonate and inhibited hydrochloric acid. Patent RU 2065942-C, 1996. 

Contact lens care products can be divided into three categories cleaners, disinfectants, and lubricants. Improperly cleaned lenses can cause discomfort, irritation, decrease in visual acuity, and giant papillary conjunctivitis (GPC). This latter condition often requires discontinuation of lens wear, at least until the symptoms clear. Deposits can also accumulate preservatives from lens care products and produce toxicity and can act as a matrix for microorganism attachment to the lens [317]. Thus, cleaning with the removal of surface debris, tear components, and contaminating microorganisms is one of the most important steps contributing to the safety and efficacy of successful lens wear [318]. 

Enzymatic cleaners contain enzymes derived from animals, plants, or microorganisms. Plant and micro-organism-derived enzymes may cause sensitization in many lens wearers [322], A list of commonly used enzymes is provided in Table 10. All of these enzymes are effective in removing deposits from the contact lens surface [323]. They are biochemical catalysts that are specific for catalyzing certain chemical reactions. Those... 

Opaque deposits in the cornea and lens may occur with chronic phenothi-azine treatment, especially with CPZ. Although visual acuity is not usually affected, periodic slit-lamp examinations are recommended with use of long-term phenothiazines. Baseline and periodic slit-lamp examinations are also recommended for quetiapine-treated patients because of cataract development and lenticular changes in animal studies. 

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