1. In a small case-control study, patients using reusable contact lenses had a 4.14 times higher risk of Acanthamoeba keratitis than those using daily disposable lenses.

2. Among daily disposable contact lens users, shorter time per day of contact lens wear, showering with contact lenses, reusing contact lenses, and wearing lenses overnight were associated with higher Acanthamoeba keratitis risk.

Evidence Rating Level: 3 (Average)

Study Rundown: Use of contact lenses increases risk for microbial keratitis, or infection of the surface of the eye. Acanthamoeba is a trophozoite that is an uncommon cause of contact lens-associated keratitis but often leads to severe infection and vision loss. This single-center case-control study aimed to identify risk factors for Acanthamoeba keratitis (AK) in contact lens users. About 80 patients diagnosed with AK were compared to about 120 controls. In a model adjusted for contact lens hygiene compliance and interval between contact lens appointments, subjects who used reusable contact lenses were 4.14 times more likely to have AK than those who used daily disposable lenses. Rigid, gas-permeable lenses were also associated with higher AK risk than daily disposable lenses. Within the group of daily disposable contact lens users, risk factors for AK were contact lens wear for less than 12 hours per day as compared to 12 hours or more, showering with contact lenses in, contact lens reuse, and overnight contact lens wear. Interpretation of these findings is limited by the small sample size, case-control study design, and use of a questionnaire subject to reporting bias. Nonetheless, the finding of a significant reduction in risk for Acanthamoeba keratitis with daily disposable contact lens use is consistent with other studies showing a benefit with respect to other keratitis-causing organisms and with research showing that lens cases may be a site for Acanthamoeba colonization. This study thus represents a point in favor of daily disposable lenses for reducing infection risk.

Click to read the study in Ophthalmology

Relevant Reading: Contact lens-related microbial keratitis: How have epidemiology and genetics helped us with pathogenesis and prophylaxis

In-Depth [case-control study]: Patients treated for AK at a single large center in England between 2011 and 2014 were included as cases. AK was diagnosed based on culture data, histopathology, consistent clinical course and treatment response, or polymerase chain reaction. Controls were contact lens users presenting to the same emergency department for unrelated diagnoses between 2014 and 2015. Risk factor assessment was based on a questionnaire. Adjusted odds ratios for daily disposable versus reusable lens use as well as independent risk factors were calculated using least absolute shrinkage and selection operator models. The adjusted odds ratio of 4.14 for reusable versus daily disposable contact lenses in AK patients as compared to controls had a 95% confidence interval of 1.92 to 8.9 (p<0.001). “British white” as compared to “other” ethnicity was identified as an independent risk factor. The median duration of contact lens per wear within the sample was 12 hours.

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