Contact Lens-Associated Microbial Keratitis
Abstract & Commentary
Synopsis: The lowest risk of microbial keratitis was found in users of rigid gas-permeable lenses.
Source: Cheng KH, et al. Incidence of contact-lens-associated microbial keratitis and its related morbidity. Lancet 1999; 354:181-185.
Most of the 28 million contact lens wearers in the United States use them for cosmetic reasons as an alternative to spectacles for correcting refractive errors, as opposed to the small number (3%) who use them for treatment of ocular surface diseases or aphakia. Microbial keratitis, which may result in permanent corneal scarring or perforation, with subsequent permanent visual loss, is the most dreaded complication of contact lens wear. It is usually due to bacteria, though fungi and acanthamoebae have also been implicated.
For this study, a prospective population study was done among all ophthalmologists in the Netherlands (n = 440), who were asked to report all cases of microbial keratitis seen over a 90-day period in 1996. During this interval, 111 cases of keratitis were identified.
Extended-wear soft contact lens (1-2 week disposables) users were almost 20 times as likely to incur microbial keratitis as users of daily-wear rigid gas-permeable lens users. Even daily-wear soft lenses were more than three times more likely to suffer microbial keratitis than rigid gas-permeable lens users. In this study, Serratia and Pseudomonas aeruginosa were the most commonly isolated bacteria; only one case of acanthamoeba infection was identified, and there were no fungal infections. Less than half of all cases had any pathogen recoverable from culture.
Infection resulted in five hospitalizations, requiring one excimer laser corneal scar excision and three cases of corneal transplantation due to visual impairment from scar. The patient with acanthamoeba progressed to visual impairment resulting in near-blindness.
Cheng and colleagues note that overnight use of lenses was the primary risk factor for corneal infection and should hence be discouraged. In this population, rigid gas-permeable lenses were associated with the least risk of microbial keratitis. (Dr. Kuritzky is Courtesy Clinical Assistant Professor, University of Florida, Gainesville, FL.)
The lowest risk of microbial keratitis among contact lens users was found in those who wear:
a. extended-wear soft contact lenses.
b. daily-wear soft contact lenses.
c. rigid gas-permeable contact lenses.
d. All of the above
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