Clinicians often debate when it is necessary to perform a corneal culture. When it comes to microbial keratitis (MK), researchers introduced the 1, 2, 3 rule in 2007. Culture when at least one of these parameters is met: >1+ anterior chamber cells, >2mm infiltrate or infiltrate <3mm distance from the corneal center. A team of researchers at Massachusetts Eye and Ear in Boston implemented this treatment algorithm, with the mandatory addition of fortified topical antibiotics after cultures are obtained—with promising results.

Their study compared MK outcomes for cases that presented two years before they implemented the updated algorithm with those who presented two years after implementation. A total of 665 cases of MK were treated before and 767 after. With approximately 60 to 70 days of follow-up, 12.9% of the first group experienced vision-threatening complications compared with 11.2% of the second group.

The researchers note the algorithm was most useful for patients who only met one of the three criteria for culture. Of these patients, 54.6% vs. 67.7% were cultured in the first and second groups, respectively, and 29.7% vs. 53.9% were prescribed fortified antibiotics. This led to better outcomes, with 9.7% of the first group experiencing a vision-threatening complication compared with just 1.8% of those treated based on the algorithm.

The study also found more cases that ultimately needed it were culture at presentation rather than delayed, and fewer cases that met none of the criteria were cultured.

“The implementation of this algorithm reduced vision-threatening complications for patients with lesions satisfying only one criterion, arguably the most difficult patients in whom to judge disease severity,” the researchers concluded in their paper. “Implementation also led to a decrease in patients receiving unnecessary care.”