To assess publications examining the occurrence, composition, and clinical significance of a microbiome at the ocular surface.
MEDLINE, EMBASE, and Google Scholar were searched. Reference lists of included articles were also searched for relevant citations. All publications up to June 1, 2019, were analyzed.
Eleven articles and 1 abstract were included, analyzing 661 patients. Articles generally report bacteria to the genus level. The presence of DNA associated with diverse bacterial species was reported including pathogenic species, such as Pseudomonas and Neisseria. Bacterial DNA that makes up the microbiome, such as Acinetobacter, Actinomyces, Aquabacterium, Bradyrhizobium, Corynebacterium, Sphingomonas, Staphylococcus, and Streptococcus, in other parts of the body was found. The putative ocular microbiome is consistent between right and left eyes and is affected by contact lens use (higher Pseudomonas levels) and blepharitis (higher Staphylococcus levels).
There is a significant likelihood that there is at least a transitory ocular surface microbiome, with Acinetobacter, Corynebacterium, Propionibacterium, Staphylococcus, and Streptococcus detected in at least 7 of 11 studies. However, further investigation attempting to control for environmental and methodological contaminants (Aquabacterium and Bradyrhizobium are commonly identified as contaminants in DNA extraction kits) is required. Bacteria, such as Propionibacterium, Staphylococcus, and Streptococcus, capable of causing sight-threatening infections may reside on a healthy ocular surface. With greater understanding, we can establish whether elements of the ocular surface microbiome are harmful or protective (despite their small quantities); furthermore, new therapeutic agents can be identified to treat and prevent ocular surface infection and inflammation.