A team of Canadian researchers found that diagnostic eye drops have a low contamination risk and the same efficacy seven months beyond the recommended period of 28 days in a controlled clinical context.

The study evaluated 38 primary eye care students who used a total of 4,971 drops of proparacaine, 3,219 drops of tropicamide and phenylephrine, and 1,896 drops of cyclopentolate. The researchers analyzed bacterial contamination at zero, two, four, six and eight weeks and three, four, five, six and seven months. They also looked at the anesthetic, mydriatic and cycloplegic effects after seven months of use.

The team did not find any bacterial or fungal contamination after the 10 inoculation sessions. They note that none of the participants reported eye infections for two weeks after they were administered drops.

The study concludes, “there was no difference in the efficacy when compared with new drops.”

Hanssens JM, Quintana-Giraldo C, Jacques S. Shelf life and efficacy of diagnostic eye drops. Optom Vis Sci. September 17, 2018. [Epub ahead of print].