Material and Method: This prospective case-control study included 52 patients with contact lens related keratitis treated between 1 December 2006 and 15 October 2007 at the Faculty of Medicine, Siriraj Hospital. Controls were sixty-three contact lens users attending with disorders unrelated to contact lens wear. All subjects with informed consent were interviewed about demographic data, types of contact lens and contact lens solutions, contact lens use past the recommended replacement date, overnight wear, and lens hygiene. Odds ratio (OR, estimates of relative risks) and 95% confidence interval (CI) were calculated through multivariable logistic regression analysis.

Results: The use of contact lens past the replacement date caused the highest risk of developing microbial keratitis (OR = 9.1; CI 1.8-45.4, p = 0.005). Overnight wear of lenses (OR = 2.9, CI 1.3-6.2, p = 0.012) and poor lens hygiene (OR = 2.3, CI 1.0-5.1, p = 0.007) significantly increased the risk of microbial keratitis, respectively. None of the other risk factors showed a significant association.

Conclusion: The significant risk factors for contact lens related microbial keratitis in the present study were the use of contact lens past the replacement date, overnight wear, and poor lens hygiene. Thus, the appropriate advice of contact lens care and usage may reduce the risk of microbial keratitis in contact lens wearers.

Keywords: Contact lens, Microbial keratitis, Risk factor, Infection