Polymer combination at root of Fusarium outbreaks, physicians say

SINGAPORE — A combination of polymers that were added to a common contact lens solution to improve comfort may be a key part in the Fusarium keratitis outbreaks that occurred earlier this year, said Donald Tan, MD, here at the Asia-Pacific Academy of Ophthalmology meeting.

Prof. Tan said the polymer film build-up in Bausch & Lomb’s ReNu contact lens solution “trapped” the Fusarium molecule that led to the significant number of outbreaks.

Prof. Tan and colleagues at the Singapore National Eye Center were the first to discover the outbreak of Fusarium and link it with contact lens solution.

“The disinfectant in [ReNu with] MoistureLoc is actually very effective,” Prof. Tan said. “The problem is when you add other things in, like the polymers to improve comfort. The polymers are actually trapping the fungus so that the disinfectant, which is very strong, cannot get at the fungus. So it is a formulation problem.”

In an interview with Ocular Surgery News, Prof. Tan said, “what Bausch & Lomb has done is clearly show a plausible sequence of events in which MoistureLoc would be more likely to cause this outbreak than other solutions and that was the three different polymers which trap the fungus in.”

This sequence of events is related to poor compliance by contact lens wearers combined with the polymer issue. Prof. Tan said Bausch & Lomb has found that the fungus can grow on the tip of an open bottle or on the cap because it’s “trapped” there by the polymers.

He added B&L found the practice of “topping off” that is common among contact lens wearers seems to have led to the cases of Fusarium. When a contact lens wearer does not rinse the used solution from the lens case before refilling it with fresh solution, the practice is called topping off, Prof. Tan explained.

Prof. Tan presented data on behalf of Bausch & Lomb during an APAO-sponsored symposium indicating that the combination of polymers in the ReNu with MoistureLoc solution builds up when the water in the solution evaporates. Fusarium can survive in the leftover build up and attach to the contact lens when it is washed out in the solution, Prof. Tan said. If the wearer topped off the solution instead of cleaning out the contact lens holder, the disinfectant in MoistureLoc “cannot break through the film and kill the bacteria,” thereby allowing it to reach the corneal surface, Prof. Tan said.

“The high polymer content combined with poor product compliance reduces the margin of safety,” he said.

Other non-compliance factors are contact users reusing solution, not rinsing contact lens cases and not cleaning or replacing lens cases.

Executives with Bausch & Lomb agreed, telling Ocular Surgery News that the formulation issue is “a result of non-compliant behaviors relating to evaporative conditions favoring polymer concentration, such as topping off, not changing solution daily and not cleaning and replacing the lens case.” In addition, there is a “causal relationship” between film build-up and non-compliant habits. B&L notes that Fusarium found on the tip of a solution with polymer film is one example of the patient not closing the cap after use as directed.

The polymer theory is part of a problem also related to the type of disinfectant molecule specifically used in MoistureLoc, Terrence O’Brien, MD, said. B&L opted to use alexidine in the MoistureLoc formulation. Alexidine is a smaller molecule than the company had previously used, Dr. O’Brien said. The smaller weight meant that absorption into the lens material is prohibited, but that also means the Fusarium bacteria can survive on the surface of the contact lens, he said.

“We don’t just need disinfectants in these solutions, we need biocompatible disinfectants,” he said.

Dr. O’Brien said case control studies are under way at Bascom Palmer Eye Institute in Miami and in sites in Singapore and Malaysia.

To date, Prof. Tan has found 68 cases of Fusarium keratitis in Singapore, and Dr. O’Brien has reported 130 confirmed cases around the United States. An additional 18 cases have been found in Malaysia at one physician’s practice, they said.

“I think we still need to clear up issues,” Prof. Tan said. “It is still surprising why there was MoisturLoc use in other countries, which did not have any infections at all, such as throughout Europe. There are still these unanswered questions. We also saw Fusarium keratitis in other contact lens solutions. This could just be ‘noise,’ but I think it’s time to also have a look at how solutions are tested and review the current guidelines.”

“Fusarium keratitis is an emerging disease, and more research must be done,” Prof. Tan said.