RISK-FACTORS FOR ACANTHAMOEBA-KERATITIS IN CONTACT-LENS USERS - A CASE-CONTROL STUDY

Objective-To investigate reasons for an increase in cases of Acanthamo eba keratitis related to contact lenses. Design-Case-control study. Ca ses were contact lens related acanthamoeba keratitis patients treated between 1 September 1989 and 31 August 1992. Controls were lens users without lens related disease who presented as new patients to the casu alty department from 1 March 1992 to 31 August 1992. All subjects comp leted a questionnaire detailing lens use and hygiene practices. Settin g-Eye hospital. Subjects-35 cases with acanthamoeba keratitis and 378 controls. Main outcome measures-Relative risks comparing different con tact lens types, socioeconomic classification, age, sex, lens use, len s wearing experience, hygiene compliance, and hygiene systems. Results -The crude relative risk for developing acanthamoeba keratitis with th e use of daily wear disposable lenses was 49.45 (95% confidence interv al 6.53 to 2227; P < 0.001) compared with conventional soft lenses (th e referent). Multivariable analysis showed that this increased risk co uld be largely attributed to lack of disinfection (relative risk 55.86 (10 to 302); P < 0.001) and use of chlorine based disinfection (14.63 (2.8 to 76); P = 0.001) compared with other chemical systems (the ref erent). None of the other outcome measures showed a significant associ ation. Conclusions-Both failure to disinfect daily wear soft contact l enses and the use of chlorine release lens disinfection systems, which have little protective effect against the organism, are major risk fa ctors for acanthamoeba keratitis. These risks have been particularly c ommon in disposable lens use. Over 80% of acanthamoeba keratitis could be avoided by the use of lens. disinfection systems that are effectiv e against the organism.