Recent randomized and nonrandomized prospective clinical trials have established risk factors for corneal infiltrates in silicone hydrogel wear (Table 7). Of note is that the risk of corneal infiltrates appears to be higher in the early period of silicone hydrogel continuous lens wear127 and in those wearing lenses for a shorter continuous period (<21 days).126 Both high limbal redness and corneal staining appear to be predictive of development of a subsequent corneal infiltrate in a multivariable analysis.121 In a pooled analysis of silicone hydrogel daily wear clinical trials, limbal redness was not associated with the subsequent development of a corneal infiltrate, however, eyes which demonstrated toxic staining related to the lens type/care solution combination had a higher risk in univariate analysis (OR 3.1×, 95% CI 1.4–6.8) than eyes without staining and the rate of such infiltrates significantly increased with degree of staining observed.125 These reports suggest that in addition to consideration of well-established risk factors, careful observation of wearers during the initial period of wear is extremely important in managing such complications. A summary of risk factors associated with sterile infiltrates is shown in Table 7.
As discussed, sterile infiltrates are a broad category that encompasses all corneal infiltrates not presumed to be associated with replicating organisms in the tissue. Such inflammatory events can be analyzed as a group as described above or separated into different categories. Although the difficulty in differentiating between clinical entities has been described,128 specific conditions with clearly different causes and manifestations within the spectrum of sterile corneal infiltrates have been recognized and described. The epidemiology of two of these groups, contact lens induced acute red eye (CLARE)129 and contact lens peripheral ulcer (CLPU)5 are described below.
CLARE is an inflammatory reaction characterized by severe conjunctival and limbal hyperemia, corneal infiltration, and pain. By definition, it occurs during EW only and usually has an early morning acute onset.5 In a study of continuously worn hydrogel lenses, 34% of patients developed contact lens acute red eye over a 12-month period.130 In studies of disposable EW use, an incidence of CLARE of 12% has been reported in India115 and 1.4% in Australia.131 When subjects were fitted with silicone hydrogel lenses, 0.8% of eyes were reported to develop a CLARE reaction in a study of 504 patients followed for a year in Sweden.117 Risk factors include high water contact lenses,129 tight fitting contact lenses,129 and a recent episode of upper respiratory tract infection.132 More recently, an association between microbial contamination of contact lenses worn overnight, particularly Gram-negative bacterial contamination, and CLARE has been reported.124 When exposed to inadvertently contaminated contact lenses, one-third of patients developed an acute inflammatory reaction during a single overnight wear period.133 In addition, Haemophilus influenzae have been cultured from the conjunctivae and contact lenses of wearers diagnosed with CLARE.131 Other Gram-negative bacteria such as Haemophilus parainfluenzae and certain Gram- positive bacteria such as Streptococcus pneumoniae have also been implicated.134 Animal models synonymous with human CLARE, showing an inflammatory response in the absence of microbial infection have been established in the presence of colonization of the contact lens by high numbers of Gram-negative bacteria.135,136
A CLPU is an acute inflammatory response characterized by small circular full-thickness epithelial lesions in the peripheral cornea, associated with stromal infiltration.137 Differentiation from infectious ulcers is based on a clinical criteria.5,27,107 Histopathological studies of biopsies taken from these lesions have shown no invasion of the stromal tissue by microorganisms.138 Like CLARE, CLPU is primarily associated with overnight wear and the incidence in disposable EW varies from 1.6 to 2.9% in Australia130 to 13%115 per year in India. The annualized rate in wearers of silicone hydrogel lenses appears similar to Australian rates at 1.1% of eyes in Sweden,117 0.3% of subjects in a large multinational study,139 1.2% of subjects in Spain,140 and 1% of wearers in the United States.120 An association between microbial contamination of contact lenses and CLPU has been demonstrated,136 although, more specifically, colonization of the contact lenses and/or the lids and conjunctiva by low numbers of the Gram-positive bacterium Staphylococcus aureus 53,141 and the Gram-negative bacteria Pseudomonas spp.132 Epithelial trauma was shown to be a significant factor for the production of CLPU in contact lens wearing rabbits141 and although unproven, may prove to be a significant factor in humans.
Contact lenses clearly have optical, occupational, sporting, and cosmetic advantages for millions of wearers; however, certain risks have been associated with their use. Given the large population currently wearing contact lenses worldwide, even rare reactions can affect large numbers of wearers. This becomes an issue for the delivery of primary eye care and for practitioners involved in the fitting of lenses and in the management of lens related disease. Differences in risk for different types of contact lenses and wearing patterns have been demonstrated for both rare and common lens related complications. This article has reviewed the epidemiology of both microbial keratitis and sterile keratitis for contemporary contact lens types.
Understanding the epidemiology of lens related disease, particularly with the introduction of new lens types and modalities, is crucial for practitioners to enable an informed choice of lens modality, wear schedule and hygiene regimes to be made. Emerging risk data have indicated that careful observation is important during the early period of lens wear and that early adopters of new technologies may show different patterns of risk. Epidemiological data also provides information on the etiology of lens related complications, which is required to enable safer lens wear modalities to be developed.
The authors thank Arthur Ho for graphical and technical assistance.
The authors are supported by the Institute for Eye Research (FS, LK, IJ, NC), the University of New South Wales (FS, LK), the Commonwealth Government through the Cooperative Research Centres Programme (Vision Cooperative Research Centre; FS, LK), and the National Health and Medical Research Council (LK).
North Wing, Gate 14, Barker St.
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