There is a risk of microbial contamination of preservative-free eye drops in multiple application containers, warn doctors in a report in the British Journal of Ophthalmology.

“Contamination of eye drops may be related to the design of multiple application containers,” Dr. M. Q. Rahman, of Tennent Institute of Ophthalmology, Glasgow, UK, and colleagues offer. A pipette attached to the cap of the bottle comes completely out of the container during administration, exposing the open contents of the bottle directly.

Content spillage may also increase the risk of contamination, according to the investigators. Another risk factor is poor technique in administering the eye drops.

Most eye drops used in the UK contain preservatives and are bottled in plastic containers. However, in certain individuals, preservative-free drops are used to avoid ocular irritation and allergies.

Of 95 eye drop bottles Rahman and colleagues tested, significant bacterial growth was observed in eight, for an overall incidence of 8.4 percent.

Contamination did not occur in any of the 53 antibiotic eye drop bottles. For the 42 non-antibiotic bottles, the overall incidence of contamination was 19 percent. The difference between the two groups was statistically significant.

A total of seven different types of organisms were identified from the eye drop bottles, including Staphylococcus aureus, a type of bacteria that is increasingly becoming resistant to standard antibiotics. Some of the contaminated bottles grew more than one type of contaminant.

“The prescription of these drops to patients with compromised ocular surface defences needs to be considered with caution,” the team concludes.

SOURCE: British Journal of Ophthalmology, February 2006.