Contact lenses, soft

In 1971, Bausch Lomb received U.S. Food and Dmg Administration approval for a soft contact lens based on the HEMA system and launched Soflens. The soft lens market has grown dramatically soft lens surpassed hard lens wear by the late 1970s, accounting for about 80% of the U.S. contact lens market in the early 1990s. 

Ocular sensitization to thimerosal has been well documented over the years [126-132]. Although thimerosal had at one time been referred to as the preservative of choice for soft contact lens care products [133-135], its use has been supplanted almost completely by the polyquaternium-1 and polybiguanide preservatives. 

This preservative is comparatively new to ophthalmic preparations and is a polymeric quaternary ammonium germicide. Its advantage over other quaternary ammonium seems to be its inability to penetrate ocular tissues, especially the cornea. It has been used at concentrations of 0.001-0.01% in contact lens solutions as well as dry eye products. At clinically effective levels of preservative, POLYQUAD is approximately 10 times less toxic than benzalkonium chloride [87,137], Various in vitro tests and in vivo evaluations substantiate the safety of this compound [137,141,142], This preservative has been extremely useful for soft contact lens solutions because it has the least propensity to adsorb onto or absorb into these lenses, and it has a practically nonexistent potential for sensitization. Its ad-sorption/absorption with high water and high ionic lenses can be resolved by carefully balancing formulation components [143],... 

M. E. Stern, H. F. Edelhauser, and J. W. Hiddemen, Methods of Evaluation of Corneal Epithelial and Endothelial Toxicity of Soft Contact Lens Preservatives. Presented at Contact Lens International Congress, Las Vegas, Nevada, March 1985. 

Goda T, Ishihara K (2006) Soft contact lens biomaterials from bioinspired phospholipid polymers. Expert Rev Med Devices 3 167-174... 

P.C. Nicolson, J. Vogt, Soft contact lens polymers An evolution, Biomaterials 22 (2001) 3273-3283. 

Observations Soft contact lens materials represent a balance between hydrophilic... 

ATR spectroscopy in the infrared has been used extensively in protein adsorption studies. Transmission IR spectra of a protein contain a wealth of conformational information. ATR-IR spectroscopy has been used to study protein adsorption from whole, flowing blood ex vivo 164). Fourier transform (FT) infrared spectra (ATR-FTIR) can be collected each 5-10 seconds165), thus making kinetic study of protein adsorption by IR possible 166). Interaction of protein with soft contact lens materials has been studied by ATR-FTIR 167). The ATR-IR method suffers from problems similar to TIRF there is no direct quantitation of the amount of protein adsorbed, although a scheme similar to the one used for intrinsic TIRF has been proposed 168) the depth of penetration is usually much larger than in any other evanescent method, i.e. up to 1000 nm water absorbs strongly in the infrared and can overwhelm the protein signal, even with spectral subtraction applied. 

Cyanoacrylate has been used for sealing corneal perforations, but it is not smooth or malleable, and it exhibits a hard tissue-scratching surface and requires the patient to use a soft contact lens for comfort. Another surgical limitation when using cyanoacrylate is the immediate polymerization on a wet or moist corneal surface, and that property reduces the time allocated for and increases the difficulty in applying the glue to a precise location in a well-controlled manner. 

Because fluorescein sodium can penetrate into many hydrogel contact lenses, the lenses become discolored, which raises bacterial growth issues and renders the lenses cosmetically objectionable. In addition, the boimd-ary between lens and tears becomes obscured, which precludes the use of fluorescein in soft contact lens fitting. Fluorexon, a molecule similar in fluorescent characteristics to that of fluorescein, is less readily absorbed by the soft lens material, which renders it useful in fitting and evaluating soft and hybrid design lenses. 

A variant of the classic form of SLK is that of soft contact lens-induced SLK. Although affected individuals typically show findings very similar to patients with SLK,... 

Figure 25-34 Irritated pinguecula adjacent to edge of a soft contact lens.

To help relieve patient discomfort due to the rupture of epithelial bullae, a therapeutic soft contact lens may be tried. Effective restoration of patient comfort and visual function for well-established Fuchs dystrophy, however, may be best achieved through penetrating keratoplasty (Figure 26-7). Fuchs dystrophy is the primary condition... 

During acute episodes a broad-spectrum topical prophylactic antibiotic ointment, such as 0.3% tobramycin or 0.5% moxifloxacin, protects the cornea from secondary infection while it heals. The use of a therapeutic contact lens and topical NSAIDs, such as diclofenac sodium 0.1% solution or ketorolac 0.5% solution, provide symptomatic relief. The therapeutic soft contact lens also protects the regenerating epithelium and temporarily provides epithelial stability. A cycloplegic agent, such as 5% homatropine, should be instilled to decrease ciliary spasm and pain. Oral analgesics can be prescribed as needed (see Chapter 7). The eye should be examined in 24 hours and the therapy continued until the epithelial defect is healed. 

If topical anesthetic abuse is suspected, discontinuation is critical. A broad-spectrum topical antibiotic such as 0.5% moxifloxacin three times daily is used to protect the disrupted corneal epithelium from secondary infection as the tissue heals. Topical NSAIDs, such as 0.1% diclofenac sodium solution or 0.5% ketorolac solution, and a therapeutic soft contact lens help to reduce pain. Cycloplegic and topical steroids are indicated if an anterior chamber reaction is present.Toxic keratitis can heal without permanent vision loss within days after discontinuing the use of the anesthetic but may result in permanent scarring, vascularization, and visual loss. Surgical treatment, such as a penetrating keratoplasty, may be necessary. 

Patients with CIE complain of pain, tearing, foreign body sensation, and photophobia. When asked, they often report a history of soft contact lens wear or staphylococcal lid disease. CIE is common in adults but is quite rare in children. 

Adapted from Baum J, Dabezies OH Jr. Pathogenesis and treatment of sterile midperipheral corneal infiltrates associated with soft contact lens use. Cornea 2000 19 777-781. 

Unlike dendritic keratitis, indolent ulcers are typically very difficult to treat. Instillation of a prophylactic antibiotic, such as polymyxin B-bacitracin ointment two to four times a day, and a cycloplegic agent, such as 5% homatropine two to three times a day, is indicated. Therapeutic soft contact lens use with appropriate antibiotic therapy can also be considered as alternatives. These patients must be monitored carefully to ensure that no secondary infection develops. If the ulcer deepens, a new infiltrate forms, or if there is an increase in the anterior chamber reaction while the patient is being treated, cultures should be performed to rule out bacterial or fungal infection. Cyanoacrylate glue, conjunctival flap surgery, or tarsorrhaphy may be required if healing does not occur. 

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. 

Adapted from Sweeney DF, Jalbert I, Convey M, et al. Clinical characterization of corneal infiltrative events observed with soft contact lens wear. Cornea 2003 22 435-442. 

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... 

The soft contact lens patient who becomes symptomatic from epithelial microcysts tends to develop symptoms rather suddenly after uneventful contact lens wear. It is not uncommon for the patient with microcysts to have been remiss in timely follow-up care, when the formation of microcysts may have been detected before symptoms developed. Symptoms associated with this condition include burning, foreign body sensation, tearing, and photophobia, all likely related to the disrupted epithelium. Decreased visual acuity results, even with the best spectacle correction in place, because of the now irregular corneal surfece. 

Figure 26-58 SubepitheUal infiltrates secondary to soft contact lens wear. (Courtesy of Pat Caroline.)...

All ages and both genders may be affected. Although study results vary widely, 3% to 15% of rigid lenses wearers and 5% to 10% of soft contact lens wearers are reported to develop GPC. Eighty-five percent of GPC occnrs in hydrogel lens wearers.The incidence of GPC is lower in those wearing disposable versus conventional contact lenses and is lower with more frequent versus less frequent lens replacement. 

Soft contact lens wearers first show papillary changes in the upper or inside edge of the tarsal plate (zone 1), followed by involvement of the middle area of the tarsal plate (zone 2), and finally progression toward the lid margin (zone 3). Rigid contact lens patients have fewer and smaller papillae that appear closer to the lid margin (zone 3) or in the central zone (zone 2) of the upper tarsal area (Figure 27-2). 

GPC develops earlier in patients wearing soft contact lenses than in those wearing rigid lenses. The reaction has been found to develop as early as 3 weeks after initiation of soft contact lens wear and may begin as early as 14 months after initiation of rigid lens wear. The average time for GPC to develop with soft lens wear is 10 months however, the interval varies depending on the study. 

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