Thermal disinfection

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. 

Soft contact lenses were introduced in the United States in 1972. At that time, the thermal disinfection method was the only method available. It uses either preserved or unpreserved saline solution. 

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. 

Water of pharmaceutical quality is used as a raw material, excipient, solvent, and as cleansing agent. In addition the pharmaceutical production facility needs water for (thermal) disinfection or sterilisation and for the preparation of pharmaceutical quality reagents [6]. 

First, it provides sanitization. This is important if the wash is undertaken at temperatures for which thermal disinfection is not possible or with residence times for which it is incomplete. Other formulation actives can also contribute to the overall biocidal activity of the composition and potentiate the kill achieved by the activated bleach system. 

In order to obtain effective low-temperature bleaching, species known as bleach activators are added to the formulation. These react with the persalt in the wash bath to produce stronger oxidants, typically peracid anions. The presence of activators not only allows effective low-temperature bleaching to be achieved but also provides sanitization at temperatures for which thermal disinfection is not possible (discussed later). Bleach activators can be described as acylating agents and they are typically esters or amides of carboxylic acids. 

At 71°C (the minimum temperature recommended by the U.K. Dept, of Health [in H.M.(71)49 for effective thermal disinfection of hospital lavmdry in a 3-min wash], all formulations achieve >99.99% kill, as expected. It is apparent, therefore, that the TAED-activated formulation at 40°C can achieve the same degree of kill as can be obtained by thermal disinfection at 71°C. 

Chemical additives are added automatically to the appropriate compartments and steam can be injected into the main wash compartments to achieve the required high temperature levels. Stains and soil are removed through a combination of mechanical action, time and temperature control, detergent action and de-staining agents, which can include bleaches. For thermal disinfection, the achievement and maintenance of the required temperature areis critical. 

OZONE. [CAS 10028-15-6]. Ozone, O3, is an allolropic form of oxygen first recognized as a unique substance in 1840. Its pungent odor is detectable at "0.01 ppm. It is thermally unstable and explosive in the gas, liquid, and solid phases. In addition to being an excellent disinfectant, ozone is a powerful oxidant not only thermodynamically, but also kinetically, and has many useful synthetic applications in research and industry. Its strong oxidizing and disinfecting properties and its innocuous... 

Since the direct estimation of microbial numbers by conventional culturing methods is time-consuming and well affected by environmental conditions (18), a simple test for the most resistant enzyme activity is appropriate on a routine basis. If enzyme activity is detected, it can be assumed that the heat treatment was inadequate (4,15). Appropriately, GFPuv can be employed as a BI in thermal processes (blanching, pasteurization, disinfection) at temperatures >75°C for products at pH > 5.5, with the inactivation of GFPuv shown to be directly related to the time of exposure to moist heat and pH. 

BDD electrodes are semiconductor electrodes with microcrystalline structure and relatively rough surfaces on the micrometric scale. Diamond-coated electrodes used for disinfection are chemically, mechanically, and thermally very resistant and show very low corrosion even under high electric charge. Diamond electrodes present no surface redox processes as known from other carbon electrodes (for example glassy carbon). 

Burch, J. D. and K. E. Thomas (1998). Water disinfection for developing countries and potential for solar thermal pasteurization. Solar Energy. 64, 1-3, 87-97. 

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... 

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. 

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