Contact lens-related microbial keratitis accounts for significant vision loss and health-care expenditures each year. Early identification and treatment can help improve prognosis, but better diagnostic methods are needed. Research to understand the effects of soft contact lenses on tear film physiology may provide new insights on pathogenesis and prevention.
Dr. Alfonso, professor and chairman, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, spoke about contact lens-related ocular infections in his delivery of the Richard L. Lindstrom, MD, Lecture during a symposium sponsored by the Contact Lens Association of Ophthalmologists.
"We know the pathogens that can cause a severe microbial keratitis can be present in the eye, the environment, the contact lens, and contact lens paraphernalia, and that lens wear itself contributes to corneal epithelial damage and creates an altered immune environment predisposing to infection," he said. "It is unlikely that a sterile lens-wear system will ever be developed, and poor patient compliance with instructions for lens wear and care will always be a risk factor."
Improved diagnosis is one strategy for reducing microbial keratitis morbidity. Currently, analysis of corneal scrapings is relied on most often, but better techniques providing microbiology results faster and with 100% specificity are needed, Dr. Alfonso said.
"This is where methods of DNA extraction and polymerase chain reaction amplification can play an important role, and we are now developing a system for analyzing specimens from the cornea and contact lens paraphernalia that offers a turnaround time of 6 hours with 100% specificity," he added.
Access to and expertise in using confocal microscopy also will be important, he said, because this technology is helpful for diagnosing fungal and Acanthamoeba infections.
Patients who present with a small peripheral ulcer mostly are treated empirically with a fluoroquinolone, but ideally, a specimen should be obtained for culture. In patients with a large peripheral or central corneal ulcer who are at risk for significant vision loss, culture is mandatory, but empiric treatment is started with a fluoroquinolone plus vancomycin considering the trend toward decreased sensitivity of Staphylococcus aureus to the fluoroquinolones.
"Steroids should be avoided until the offending organism can be identified and treated, as they can enhance the growth of Fusarium and amoebic organisms," Dr. Alfonso said. "Surgical therapy is important in the management of infections caused by some of the more difficult-to-treat organisms."
Recognition that soft contact lens wear is associated with a much higher risk for these infections than hard contact lens wear, even though hard contacts are more likely to cause epithelial injury and are less frequently replaced, led Dr. Alfonso and co-workers to investigate possible differences between these two types of lenses with respect to effects on tear film physiology. Using high-resolution optical coherence tomography to evaluate the tear film with a contact lens present suggests that the difference between the lenses is a factor.
"The soft contact lens drapes over the limbus, trapping the tear film between the contact lens and the corneal epithelium, not allowing any significant exchange," he said. "This essentially creates a cesspool of microbes in this stagnant tear film. This leads to an interference of the normal exchange dynamics that provide natural defense mechanisms for inhibiting microbial growth."
To gain further insight into the immunology of the tear film and how it is altered by soft contact lens wear, Dr. Alfonso and colleagues have developed a rodent model of contact lens-related keratitis that they plan to use in their research.