Contact lens materials, properties requiring

Contact lenses are the most common polymer product in ophthalmology. The basic requirements for this type of materials are (T)excellent optical properties with a refractive index similar to cornea good wettability and oxygen permeability ( ) biologically inert, degradation resistant and not chemically reactive to the transfer area ( ) with certain mechanical strength for intensive processing and stain and precipitation prevention. The common used contact lens material includes poly-P-hydroxy ethyl methacrylate, poly-P-hydroxy ethyl methacrylate-N-vinyl pyrrolidone, poly-P-hydroxy ethyl methacrylate, Poly-P-hydroxy ethyl methacrylate - methyl amyl acrylate and polymethyl methacrylate ester-N-vinyl pyrrolidone, etc. The artificial cornea can be prepared by silicon rubber, poly methyl... 

The design of new polymeric materials for contact lens application requires an extensive knowledge of polymer chemistry, polymer properties and the physiology of the eye (1-4). The properties that must be optimized in designing a new contact lens material are optical transparency, chemical and thermjd stability, wettability to tears, mechanical properties, dimensional stability, biol( cal compatibility and oxygen permeability. 

The solubility parameter method (31) can be used to calculate an estimate of oxygen solubility in the swollen polymer gel. Models for the difiusion of a gas through a swollen polymer gel are available but require large amounts of computer time (26). With both pieces of data for the permeability available, the capacity of different formulations to pass oxygen to the eye can be estimated. This provides a final numerical scrcerring for the possible formulations of contact lens material. Materials which pass all of the numerical criteria can then be synthesized in the lab and the correlation of predicted properties and measured properties determined. This capacity to estimate some of the properties of a proposed polymer composition (31,32) has sharply increased the capacity of research workers to develop new materials or fit formulations to new applications in a very short time. 

Personnel involved in the handling of methanol require eye and skin protection from the irritating properties of methanol in the event of a spill. Contact lenses should not be worn, since plastic lens materials may absorb and concentrate methanol against the eye. Additional respiratory protection is not required with adequate local explosion-proof ventilation. 

Not every polymer can be manufactured successfully into a contact lens. Several important properties for both ocular physiology and patient handling are required of a material for a contact lens appHcation (1,11). In addition, the type of lens appHcation, ie, rigid, flexible, or soft, will dictate the range and importance of the key properties. 

The object of the research described in this chapter was modification of the surface properties of polymers for potential use in contact lens applications. Surface modification by an in situ approach required the addition of a surface-active material to the contact lens monomer formulation. During the cast molding operation, this surface-active material should concentrate at the monomer mix-mold interface. If the surface-active agent was polymerizable, the surface properties of the resultant contact lens would be a function of the chemistry of the surface-active material. 

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