Federal health investigators narrowed the cause of a mysterious outbreak of a potentially blinding eye fungus that affected scores of people earlier this year to poor hygiene practices and a cleaning solution made by Bausch & Lomb.

The report, in this week’s Journal of the American Medical Assn., said there were 164 confirmed cases. Users of the ReNu with MoistureLoc solution were 20 times more likely to get the infection than people who did not use that brand.

“We found that overwhelmingly MoistureLoc contact lens solution posed a high risk,” said Dr. Benjamin J. Park, an epidemiologist on the investigative team at the Centers for Disease Control and Prevention. “The source of the infection was people’s homes.”

Park said the “genetic diversity” of the fungus, Fusarium keratitis, they found after tests of contact lens cases, the factory and unopened bottles indicated that improper care contributed to the outbreak.

Dr. Marcelle Morcos, chief of ophthalmology at the Nassau University Medical Center, said eye care experts speculate that a special disinfectant in the solution was the culprit.

“When it dries a little on the cornea it could be a good medium for the fungus to grow,” Morcos said. “There could have also been outside contamination.”