Reducing oral contamination during corneal scrapes

Chameen Samarawickrama, Yi-Chiao Li, Nicole Carnt, Mark Willcox, Debarun Dutta, Stephanie Watson

Research output: Contribution to journalArticlepeer-review


Aims: To identify potential contaminants of the corneal sampling procedure and examine the effect of wearing surgical face masks on the rate of contamination.

Methods: Ten surgeons recited out loud a 30 s standardised script for corneal scraping with blood agar plates positioned 30 cm away from them. Three groups were identified: in group 1 a surgical mask was worn; group 2 had no mask worn; and group 3 had no mask but used agar plates pretreated with 5% povidone-iodine as a negative control. Each surgeon repeated the process 10 times for all groups, totalling 30 plates per surgeon and 300 plates for the experiment. All plates were masked and incubated aerobically at 37°C for 24 hours, and the number of colony forming units (CFUs) was determined.

Results: At 24 hours, group 1 had a mean of 0.3 CFUs per surgeon; group 2 had 6.4 CFUs per surgeon and group 3 had 0.1 CFUs per surgeon. The difference between group 1 and group 2 was significant (p<0.001) whereas the difference between group 1 and group 3 was non-significant (p=0.4). Use of face masks decreased the number of plates with CFUs by 93% (from 29 to 2 plates) and decreased the total number of CFUs by 95% (from 63 to 3 CFUs). The most common microbiota identified was Streptococcus species.

Conclusions: Oral bacterial microbiota may contaminate the slides and media used to collect samples during corneal sampling. Use of a face mask can significantly decrease the rate of contamination of such samples.

Original languageEnglish
Article numbere000044
JournalBMJ Open Ophthalmology
Issue number1
Publication statusPublished - 25 Feb 2017

Bibliographical note

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:


Dive into the research topics of 'Reducing oral contamination during corneal scrapes'. Together they form a unique fingerprint.

Cite this