Extended wear

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. 

Classe JG, Harris MG. Liability and extended wear contact lenses. J Am OptomAssoc 1987 58 848-854. 

Topical CsA (2%) is a beneficial therapy for symptomatic treatment ofThygeson s superficial punctate keratitis. Topical corticosteroids are generally the first line of treatment. Secondary therapy includes extended-wear contact lenses and CsA. CsA, however, has been shown to be beneficial when used as the primary treatment. In one study long-term use of 2% topical CsA in olive oil (four times a day for 3 months followed by twice daily treatment for 1 month) was evaluated in eight Thygeson s ... 

It is important to differentiate between true infection of the corneal tissue and CIE (Table 26-4). The examiner must look for signs of bacterial corneal ulcers such as discharge or anterior chamber reaction and evaluate the patient s history for risk fectors known to be associated with bacterial keratitis.These risk fectors include extended wear of contact lenses, contaminated ophthalmic solutions, poor personal hygiene, diabetes melhtus, recent... 

Acanthamoeba ocular infection was first described in 1915. Acanthamoeba keratitis can occur in both healthy and immunocompromised individuals and is initiated by contact with contaminated water. Most Acanthamoeba keratitis cases described in the mid-1980s involved daily-wear soft contact lens wearers who were using saline made from distilled water and salt tablets. Cases have also been described in extended-wear soft contact lens wearers and rigid contact lens wearers. In a survey of corneal specialists, it was found that 85% of the reported cases were in contact lens patients using primarily daily-wear or extended-wear soft lenses. 

Epithelial microcysts are an abnormal corneal response at the cellular level to chronic hypoxia from contact lens wear. When present, they tend to be observed in soft contact lens wearers, particularly those wearing extended-wear lenses. A hypoxic state can result in the development of microcysts due to such causes as... 

Most of the cleaners marketed are out-of-the-eye cleaners however, in recent years there has been a trend to try to develop cleaners for use while the lenses are inserted. A specific instance where such products could be beneficial is the case of the extended-wear lenses, which are not removed daily but are worn up to a week at a time. Generally, these cleaners are less effective in removing deposits already formed on the lens surface. However, they may play a role in retarding deposit formation. 

Hartstein, J., Ed. Extended Wear Lenses for Aphakia and Myopia, The C.V. Mosby Company St. Louis, 1982. 

Soft contact lenses, especially extended-wear lenses, carry a significantly higher risk of keratitis than hard lenses do. In a case-control stndy, the relative risk for overnight wear soft lenses was 21, for daily-wear soft lenses 3.6, and for polymethylmethacrylate hard lenses 1.3, as compared with gas-permeable hard lenses (5). 

The risk can be greatly rednced by avoiding overnight wear of the lenses (2,3). In one stndy extended wear was... 

Schein OD, Glynn RJ, Poggio EC, Seddon JM, Kenyon KR. The relative risk of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. A case-... 

EWSCLs extended-wear soft contact lenses... 

Fig. 4. (Photo)-Rigid oxygen permeable contact lenses and a new generation extended wear hydrogel lens incorporate a variety of organosilicon substituted monomers (courtesy L. Seidner, Permeable Technologies).

Workrite constructs our flame-resistant garments for maximum durability and extended wear life. 

Many materials are employed in the production of soft contact lenses. The material with the widest application in the industry is HEM A [13]. HEM A became a popular soft contact lens because of its clarity, comfort, good vision, and excellent wetting characteristics. HEMA is a hydrogel, and hydrogels are cross-linked polymer networks that are swollen in water. Hydrogels are typically classified by whether they are neutral or ionic. Anyone who has had a piece of dirt in the eye understands the need for good wettability when it comes to a contact lens. The wettability of a soft contact lens in the ocular environment is a function of the surface chemistry while it is hydrated, which determines the biocompatibility of the lens [6]. A lens surface that does not wet will cau.se discomfort and potentially increased deposits. These deposits can affect vision and the physical properties of the lens [3,4]. The major drawback of HEMA is the permeability of the material to oxygen [12]. Extended wear can result in increased vascularization of the cornea... 

Leahy, C. D., Mandell, R. B., and Lin, S. T., Do disposable lenses solve the problems of extended wear Contact Lens Spectrum, April (1989). 

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