Eye Microbiome Reduces the Severity of the Dry Eye by inhibiting the Microbiota, Implicated in the Inflammatory Response.

The ocular surface is protected by a tear film and harbors a variety of microorganisms, including bacteria, fungi, and viruses. Dysbiosis of ocular microbiome can cause ocular diseases such as conjunctivitis, keratitis, and dry eye. Several studies have indicated a correlation between microbiota composition and dry eye, with the microbiome playing a potential role in ocular surface immune responses. However, most studies analyzed using the 16S rRNA gene without detailing functional potentials, while few studies investigated the longitudinal alteration of the microbiome by therapeutic eye drops. In this study, we employed whole metagenome sequencing to analyze the longitudinal alterations of the ocular microbiome during the treatment of dry eye with cyclosporine (13 patients) and newhyaluni (13 patients). Streptococcus lividans and Streptococcus pseudintermedius increased during the treatment, and they can inhibit the microbiota related to cytokine and sphingolipid metabolic pathways. These might be related to the reduced inflammatory response and alleviated severity of dry eyes. Our findings suggest that ocular microbiome can play roles in the reduction of the inflammatory response in patients with dry eye during treatment.