Microbial keratitis is the most serious, and only potentially blinding complication of contact lens wear. To further understand and reduce the risk of this disease, incidence rates and risk factors have been estimated in numerous studies. Since these studies were conducted, new lens types have been introduced designed to reduce the risk of infection. It was hypothesised that the issues of contact lens related hypoxia and poor lens hygiene could be addressed by the introduction of silicone hydrogel and daily disposable lenses respectively. This thesis describes the incidence of and risk factors for contact lens related microbial keratitis in Australia and New Zealand. The incidence of infection was determined by capturing all cases of contact lens related presumed microbial keratitis in a 12-month surveillance study, and by estimating the number of lens wearers using a population-based phone survey. Characteristics of the cases and controls were compared to estimate risk factors. In Australia, rates of infection with daily and overnight wear of hydrogel lenses were similar to previously published reports (1.9 [95%CI]:1.8-2.0] and 19.5 [95%CI:14.6-29.5] per 10,000 wearers respectively). Compared to the incidence of infection with hydrogel lenses, silicone hydrogel lenses had a higher rate in daily wear (11.9 [95%CI: 10.0-14.6]), and a similar rate in extended wear (19.5 [95%CI:14.6-29.5]). Daily disposable lenses had a similar rate of infection to daily wear of hydrogel lenses (2.0 [95%CI:1.7-2.4]), but appeared to reduce the incidence of severe or vision loss keratitis (0.5 [95%CI: 0.5-0.6] and 0.0 [95%CI: 0.0-0.0] respectively). Conducting the study in New Zealand confirmed the increase in incidence for overnight use of lenses, irrespective of lens type. Comparison of the incidence rates in New Zealand and Australia show that the rates in the two countries are comparable, bar an unexplained lower rate of infection for extended wear of soft hydrogel lenses in New Zealand. Risk factors for infection were overnight use of lenses, from occasional overnight to extended wear use, poor lens case hygiene, smoking, high socio-economic status and less than 6 months experience in current lens type. Amongst daily wearers, Internet or mail order purchasing of lenses was also associated with a higher risk of infection. This study is unique in terms of the study design and sample size, and the wide scope of risk factors considered. The determination of these incidence rates of infection and identification of risk factors is of extreme value to lens wearers and lens care practitioners around the world, particularly as the strongest and most prevalent risk factors are modifiable.
| Identifer | oai:union.ndltd.org:ADTP/222382 |
| Date | January 2008 |
| Creators | Edwards, Catherine Patrice, Optometry & Vision Science, Faculty of Science, UNSW |
| Publisher | Publisher:University of New South Wales. Optometry & Vision Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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