Preservatives found in glaucoma eye drops have been shown to have a harmful impact on the ocular surface. They can also increase the risk of glaucoma surgery, a recent study suggests.

The study divided 12,454 patients who used glaucoma eye drops into three groups depending on the level of preservative exposure during the follow-up period (average of 4.1 years): no preservatives, mixed therapy and all preserved drops.

The researchers found that, overall, 1.9% of patients underwent glaucoma surgery during follow-up. They noted that the risk of surgery was nearly four times higher for the mixed group and nearly eight times higher for the all-preserved group compared with the group who used all preservative-free therapy.

“While these data might be used to support the consideration of routine use of preservative-free drops, in the absence of a randomized clinical trial, they cannot prove a direct cause-and-effect relationship between preservative-free glaucoma eye drops and further glaucoma surgery,” the study authors concluded in their paper.