Glaucoma is the second-leading cause of blindness in the world, with about 12.5 million of the world’s 36 million people with blindness losing their sight as a result of the condition. The only current approved strategy for treating glaucoma is to lower patients’ intraocular pressure (IOP). Medicated eye drops are most ophthalmologists’ firstline therapy.  

Preservatives are commonly used in eye drops to minimize bacterial contamination inside the bottle. The few available preservative-free formulations have recently become more popular, however, because they are thought to be better tolerated, and have fewer negative side effects. 

A recent meta-analysis of existing literature investigated whether or not preservative-free eye drops are actually safer and as effective than those containing preservatives. 

What They Did

To conduct the analysis, researchers compared data from seven randomized clinical trials (RCTs) to see how preservative-free beta-blockers performed against those containing preservatives. The studies involved 1,125 glaucoma patients. In five studies, participants were treated solely with the beta-blocker timolol. In the other two studies, patients were given timolol in combination with either bimatoprost (a prostaglandin) or dorzolamide (a carbonic anhydrase inhibitor). Follow-up periods in the studies varied.

The primary outcome of interest for the analysis was the average difference in IOP change from baseline to follow-up between those treated with preserved eye drops and those treated with preservative-free drops. Secondary outcomes included ocular side effects, and other clinical and quality of life changes.

What They Found

Differences between the preservative and preservative-free groups were minimal. The average change in IOP between the two groups was 0.29 mm Hg.

Three studies, with a follow-up time of 12 weeks, reported side effects such as irritation, and burning and stinging sensations in:

• 23.8% of patients in the preservative-free group
• 26.7% of patients in the preservative group 

There were no demonstrations of any other clinical or quality outcomes of interest. significant clinical or quality of life outcomes to favor one treatment over the other.

What it Means

Ultimately, the average change in IOP as a result of the preservative-free and preserved eye drops was not clinically relevant. Even the adverse events experienced by patients were inconclusive due to the inconsistent manner in which they were reported by the various study authors. More research would be necessary to discern any differences that might strongly recommend one treatment over the other.

“This meta-analysis did not find a definitive answer regarding the use of preservative versus preservative-free eye drops for safety,” the reviewers wrote. “The increasing use of preservative-free drops may be associated with better ocular surface and tolerability, but better evidence from clinical trials is needed.”

*Kaltwasser, J. (2021, June 30). Preservative-Free Beta-blockers Appear to Hold Up Well Against Preserved Formulations in Treating Glaucoma. American Journal of Managed Care. https://www.ajmc.com/view/preservative-free-beta-blockers-appear-to-hold-up-well-against-preserved-formulations-in-treating-glaucoma