Contact lens, manufacture

The number of contact lens wearers has grown to an estimated 24 million in the United States and 50 million worldwide. Concurrendy, there has been a proliferation of contact lens manufacturers and products. The 1980s saw the widespread introduction of lens products made of more oxygen-permeable materials, ie, rigid gas-permeable (RGP) materials that made PMMA lenses virtually obsolete and high water content hydrogels that competed with HEMA-based lenses. 

Submerged Wetting Angle", Contact Lens Manufacturers Assoc., Chicago, adopted February, 1981. 

The Effect of Crosslinker Concentration on the Rate of Polymerization. Ethylene glycol dimethacrylate is used most frequently as the crosslinker for HEMA formulations useful in contact lens manufacturing. To demonstrate the effect of crosslinker concentration on the curing rate, formulations derived from HEMA/Glycerine/BME at 85/15/0.17, while varying EGDMA (from 0.34 to 0.68), the peak times were about the same (3.73 and 3.61 minutes respectively). This is reasonable due to the similarity in molecular structure of the crosslinker and the monomer, and the low amount of crosslinker used. The possible presence of other crosslinker, such as the dimerization product of HEMA, is even less a factor to be considered in polymerization kinetics, due to low concentration (normally much less than 0.1 %, in-house information). 

CLMA Standards Subcommittee, Technical Affairs Committee (Q.A. Cappelli, chair). Industry Accepted Reference Procedure for Determining Wetting Angle 1979, 4 (4), 35-39, Contact Lens Manufacturers Association (CLMA), Chicago [cf. Contact Lens Forum],... 

Routledge R. Possible hazard of contact lens manufacture [letter]. BrMed 1973 1 487-488. 

FDA. 1989. Guidelines to contact lens manufacturers Preservative uptake/release procedures. Chem. Appendix B. Rockville, Md., USA Food and Drug Administration. 

R. Hill, Contact Lens Manufactures Association, 1981, Paper 10-81,240. 

KittreU, J. R., Quinlan, C. W., Shepanzyk, J. W., Thotocatalytic Destruction of Hexane Eliminates Emissions in Contact Lens Manufacture , Emerging Solutions in VOC Air Toxics Control, Proc. Spec. Conf. (1996), pp. 389-398. 

Soft contact lens manufacturing Silicon-chip manufacturing Cabin crew of long distance airplanes Resident staff in hospitals and hotels Travelling salesmen (from automobile heaters)... 

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. 

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. 

Contact lenses are optical devices that are either fabricated from preformed polymers or polymerized during lens manufacture. The main purpose of contact lenses is to correct defective vision. For this application, they are called cosmetic lenses. Contact lenses used medically for the treatment of certain corneal diseases are called bandage lenses. 

Polyesters synthesized from terephthaloyl chloride and isohexides were prepared, and characterized by differential scanning calorimetry, n.m.r. spectroscopy, and viscosity measurement.25,128 Another polyester, prepared by copolymerization of (2-hydroxyethyl)methacrylate with isoman-nide dimethacrylate (172), forms a hydrogel when allowed to swell in isotonic sodium chloride solution. This gel has useful properties for manufacturing contact-lens material.265... 

Contact urticaria from papain has been reported by Baur et al. (1982) in papain workers, and from contact-lens cleansing solutions by Bernstein et al. (1984), Santucci et al. (1985) and Podmore and Storrs (1989). Papain persists in the soft lens matrix despite careful rinsing (Fichman et al. 1978). In a factory manufacturing papain, Baur et al. (1982) reported that 17 of 33 workers developed type-i reactions such as periorbital edema, conjunctival irritation or allergic asthma. 

This chapter will examine the production of one particular biomedical device soft contact lenses. The surface properties of soft contact lenses influence the biocompatibility of the lens, or the ability of the material to perform with the appropriate host response in a specific application [1]. Three case studies will be u.sed to exemplify how surface science is utilized in the soft contact lens market. The case studies will examine methods of producing surfaces for biocompatible high-performance soft contact lenses as well as alterations in surface chemistry and morphology caused by manufacturing methods used to produce the lens. However, first it would be appropriate to provide some history, design goals, and background on soft contact lenses. 

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