Reducing oral contamination during corneal scrapes


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.

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Divisions: College of Health & Life Sciences > School of Optometry > Optometry
Additional Information: 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:
Publication ISSN: 2397-3269
Last Modified: 11 Dec 2023 08:19
Date Deposited: 09 Apr 2019 07:55
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Related URLs: https://bmjopht ... ent/1/1/e000044 (Publisher URL)
PURE Output Type: Article
Published Date: 2017-02-25
Accepted Date: 2016-12-24
Authors: Samarawickrama, Chameen
Li, Yi-Chiao
Carnt, Nicole
Willcox, Mark
Dutta, Debarun (ORCID Profile 0000-0002-2204-5272)
Watson, Stephanie


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