Lens disinfection

Borazjani RN, May LL, Noble JA, et al. Flow cytometry for determination of the efficacy of contact lens disinfecting solutions against Acanthamoeba spp. Appl Environ Microbiol 2000 66(3) 1057-1061. 

Marketed lens care products fall mainly into the following categories cleaners, disinfectants, lubricants, and multipurpose products. Cleaners are subdivided into daily or weekly cleaners. Disinfectants comprise solutions containing chemical antimicrobial agents, which do not require heating the lenses, and preserved or unpreserved saline solutions, which are used with an electrical thermal device for lens disinfection. These products are also used to rinse contact lenses. Lens lubricants are intended to enhance the comfort of lens wear and are used prior to insertion and during wear. Multipurpose solutions are intended to accomplish... 

Gavin, J. Button, N. F Watson-Craik, I. A. Logan, N. A. Observation of soft contact lens disinfection with fluorescent metabolic stains. Appl. Environ. Microbiol. 2000, 66, 874—875. 

To remain safe and efficacious on the eye, contact lenses must maintain clear and wetted surfaces, provide an adequate supply of atmospheric oxygen to and adequate expulsion of carbon dioxide from the cornea, allow adequate flow of the eye s tear fluid, and avoid excessive abrasion of the ocular surface or eyeflds, all under a variety of environmental conditions. The clinical performance of a contact lens is controlled by the nature of the lens material the lens design the method and quaUty of manufacture the lens parameters or specifications prescribed by the practitioner and the cleaning, disinfection, and wearing procedures used by the patient. 

The strength of a hydrophilic lens material determines how well the material survives the patient s handling, cleaning, and disinfection regimen. Materials with higher Dk have been found to be generally more fragile (31). 

Most contact lenses are worn for optical reasons as an alternative to spectacles. Contact lenses are of two types, namely hard lenses, which are hydrophobic, and soft lenses, which may be either hydrophilic or hydrophobic. The surfaces of lenses mnst be wetted before nse, and wetting solntions (section 4.5.1) are nsed for this pnrpose. Hard and, more especially, soft lenses become heavily contantinated with protein material dnring nse and must therefore be cleaned (section 4.5.2) before disinfection (section 4.5.3). Contact lenses are potential sonrees of eye infection and conseqnentiy nticroorganisms should be removed before the lens is again inserted into the eye. Lenses mnst also be clean and easily wettable by the lacrimal secretions. Contact-lens solntions are thns sterile solutions of the varions types described below. Apart fiom... 

This preservative is also comparatively new to ophthalmic formulations and has been used as a disinfectant in contact lens solutions. Polyaminopropyl biguanide (polyhexamethyl biguanide) also is a polymeric compound that has a low toxicity potential at the concentrations generally used in these solutions [141, 149, 150]. 

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]. 

Peroxides are very toxic to the cornea of the eye. After the disinfection cycle, and before placing the lens in the eye, hydrogen peroxide must be completely neutralized by reducing agents, catalase, or transition metals, such as platinum. 

In the control of chlorine disinfectant systems, the effective use of the chlorine for its intended purpose is assumed if the treated water considerably downstream from the chlorinalor contains a residual of chlorine. Depending upon use. lull-contact tinte may be assumed alter len miuules. or the interval may be extended lo several hnurs. The systems also are usually carefully monitored by bacteriological testing. Normally a dose of I lo 2 milligrams of chlorine per liter is adequate lo destroy all bacteria and leave an effective residual. Residuals of 0.1 to 0.2 milligrams per liter are usually maintained in the diluent streams front water-treatment plants as a factor of safely for consumers. 

In addition, assessment of the patient s contact lens cleaning regimen is also important. Cleaning regimen, once a critical component to lens care, has been eliminated with daily disposable lens replacement and has evolved with frequent lens replacement. Daily cleaning is essential, and when applicable, disinfection with a hydrogen peroxide system may still be an important consideration.The use of enzymatic cleaning has diminished because disposable lenses have replaced the need for it, but it may be a consideration in select cases. 

Contact lenses are made of polymeric materials designed and fabricated to correct vision. Because these lenses are removed from the eye after a prescribed wear time, lens care products are required to clean, disinfect and rinse them prior to reinsertion to avoid ocular infections and other complications. Lens care products are also required to enhance the comfort of lens wear. 

Contact lenses and their cases are frequently contaminated by microbes. Although studies have indicated that as many at 30% of lens cases are contaminated, the incidence of permanent ocular damage due to this is very low. Nevertheless, it is critical to properly instruct lens wearers and emphasize the importance of disinfection in order to avoid the potential risk of ocular infection or damage to the eyesight. 

Both thermal and chemical methods are commonly used for the disinfection of soft contact lenses. With the former, a case containing the lenses immersed in saline solution is heated by an electrical unit with a predesigned heating cycle. The current FDA requirement for thermal disinfection by saline solution requires a minimum temperature of 80° C for 10 min within the contact lens case. This ensures elimination of vegetative forms of ocular pathogens but not the spores. 

Chemical disinfection, on the other hand, is not as effective in killing organisms as thermal disinfection, but has several advantages It is simple to use, thereby ensuring greater user compliance. Lens life is longer with chemical disinfection as lenses are not subjected to daily heat treatment. The method results in fewer deposit problems as surface debris left on the lens surface due to improper cleaning is not baked by heat. 

The choice between thermal and chemical disinfection depends, to a large extent, on the recommendation of the lens practitioners. Factors involved include the wearer s sensitivity to preservatives, needs, personal hygiene habits, and product cost. Today fewer heat disinfection units are available. 

Both preserved and unpreserved saline solutions are multifunctional solutions. In addition to thermal disinfection, they are also used to dissolve enzyme tablets in cleaning contact lenses, as a rinsing solution following cleaning and chemical disinfection, and as a lens storage solution. 

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