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Infectious keratitis risk increases with extended contact lens wear
Effective treatment hinges on early and accurate diagnosis of Staphylococcus, Pseudomonas, Acanthamoeba and fungal infections.
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ATLANTIC CITY, N.J. — Contact lens-associated keratitis is rare, but the risk of infection increases significantly with extended wear, a speaker said here.
Infection related to contact lenses is not common, Douglas R. Lazzaro, MD, said at the SUNY Downstate Current Concepts in Ophthalmology meeting. “There have been a lot of studies going back almost 30 years. The risk is about five to 20 cases per 10,000 daily-wear users.”
Lazzaro cited a study showing that the risk of infectious keratitis is increased 10 to 15 times among patients who use extended-wear lenses.
Risk factors for contact lens-associated infectious keratitis include hypoxia, inappropriate lens fit and extended wear. Diabetes, steroids and tobacco use also increase the risk of contact lens-associated infectious keratitis, Lazzaro said.
Douglas R. Lazzaro
Staphylococcus, Pseudomonas and fungus
Staphylococcus and Pseudomonas are the most common organisms causing contact lens-related infectious keratitis, Lazzaro said. Fungal infections are also known to cause infection, but uncommonly.
Staphylococcus is characterized by cream-colored infiltrates and may produce necrosis of corneal cells, he said.
Staphylococcus generally responds well to fourth-generation fluoroquinolones, but methicillin-resistant Staphylococcus aureus (MRSA) has a variable response. All Staphylococcus species respond to vancomycin, he said.
Pseudomonas infection is preceded by corneal abrasions and may lead to suppurative infections.
Lazzaro said that Pseudomonas has shown resistance to fluoroquinolones and aminoglycosides in some studies and can produce a biofilm that makes it very resistant to antimicrobial agents.
“The bacteria that cause contact lens-associated keratitis form a layer of material that makes the antibiotic that you may use to treat this harder to access and actually kill the bacteria,” Lazzaro said. “Pseudomonas is known to have a very robust bacterial biofilm, sometimes making it very difficult to treat the infection.”
Fungal infections are typically limited to tropical or subtropical areas and account for only 1% of contact lens-associated keratitis cases in New York, Lazzaro said. The fungal species most commonly associated with infection is Fusarium solani, which is found on decaying vegetation, he said.
“You need to diagnose fungus early. Have a high clinical suspicion, and look for ulcers with fluffy edges and satellite lesions that don’t respond to your traditional antibacterial treatments,” Lazzaro said.
He recommended treating fungal infections with topical natamycin or amphotericin and to consider combining the topical therapy with a systemic antifungal medication, as well, if an adequate response to the local treatment is not seen.
Acanthamoeba keratitis
Acanthamoeba infection is rare, accounting for approximately 70 to 120 cases in the U.S. annually, Lazzaro said. It commonly presents with epithelial irregularities, small erosions, stromal infiltrates and pain that exceeds clinical appearance.
Lazzaro stressed the need to avoid mistaking Acanthamoeba for herpes simplex virus (HSV).
“In a number of studies, it’s been shown that Acanthamoeba early on can be dendritiform and can be incorrectly diagnosed,” Lazzaro said. “HSV almost never occurs in the setting of contact lens-associated keratitis.”
Effective treatments for Acanthamoeba include propamidine, brolene or brolene equivalent in combination with polyhexamethylene biguanide (PHMB) or chlorhexidine.
Neosporin can be added as an adjunctive therapy, and systemic therapy should be considered, he said.
“One study compared monotherapy PHMB with chlorhexidine, and there was no difference in end results,” Lazzaro said. “For Acanthamoeba, diagnose early and treat aggressively for an extended period of time with multiple drug combinations.”
Data on corneal collagen cross-linking in the treatment of Acanthamoeba are inconclusive, Lazzaro said.
Penetrating keratoplasty may be indicated when medical treatment fails, he said. – by Matt Hasson