Eyeworld

22 July 2018 EW NEWS & OPINION by Vanessa Caceres EyeWorld Contributing Writer is compelling evidence that those who wear contact lenses do have an alteration with more types and prev- alence of bacteria than those who do not," Dr. Wang said. The effect of contact lenses is just one way that the ocular surface microbiome may be affected. "The ocular surface microbiome can be altered by a variety of mechanisms, such as environmental changes, pathological states that include dry eye syndrome, contact lens wear, keratoprosthesis, use of topical antibiotics, and infection," said Rupa Shah, MD, ReVision Cataract and Refractive Surgery, Columbus, Ohio. "Clinically, this can present as contact lens-associated infiltrates, blepharitis, and postoperative infec- tions such as endophthalmitis." There is even research that is connecting the microbiomes of other areas of the body to the patho- physiology of ophthalmic diseases, Dr. Shah said, giving the example of the oral microbiome and a link to glaucoma and the intestinal micro- biome and uveitis. 4,5 EW References 1. Lu LJ, Liu J. Human microbiota and ophthalmic disease. Yale J Biol Med. 2016;89:325–330. 2. Ozkan J, et al. Temporal stability and com- position of the ocular surface microbiome. Sci Rep. 2017;7:9880. 3. St Leger AJ, et al. An ocular commensal protects against corneal infection by driving an interleukin-17 response from mucosal Ɣδ T cells. Immunity. 2017;47:148–158. 4. Astafurov K, et al. Oral microbiome link to neurodegeneration in glaucoma. PloS One. 2014;9:e104416. 5. Rosenbaum JT, et al. The microbiome, HLA, and the pathogenesis of uveitis. Jpn J Ophthalmol. 2016;60:1–6. Editors' note: The physicians have no financial interests related to their comments. Contact information Park: lisa.park@columbia.edu Shah: rupas@revisioneyes.com Wang: drwang@wangvisioninstitute.com the treatment and prevention of ophthalmic diseases," Drs. Lu and Liu wrote in their article. 1 The research is slow to emerge, and most of it has centered on the characterization of the ocular biome, to determine if there are commonalities between the bacteria that live on a healthy cornea, Dr. Wang observed. "For the most part, this research has demonstrated that comparatively, there are much fewer types and number of bacteria on the ocular surface than other areas such as the skin or gut," he said. "Also, the composition seems to appear much more variable between individuals than other areas of the body." One example related to this was an investigation of the con- junctiva of 45 healthy subjects who were sampled over 3 months and processed using culture-dependent and culture-independent methods. 2 The study found a low diversity of microorganisms and no unique- ly ocular taxa that occurred in all individuals. This may indicate that the ocular surface does not support a substantial core microbiome, Dr. Park said. "However, some individ- uals did demonstrate consistent species, suggesting the possibility of an individual-specific core microbi- ome," she said. Another study discovered that when Corynebacterium mastitidis was cultured with immune cells from the conjunctiva in mice, it induced the production of interleukin-17. 3 When the mice were treated with an antibiotic to kill C. mast and chal- lenged with Candida albicans, the mice receiving the antibiotics had a lower immune response and could not eliminate the C. albicans. This led to ocular infection. By contrast, the mice with normal C. mast could fend off the fungus. "This result is an extremely interesting one that has far-reaching implications for future eye thera- pies," Dr. Park said. There also has been research focused on how contact lenses can alter the microbiome. "There use of polymerase chain reaction to amplify genomic material from mi- crobes that have been undetectable by traditional culture techniques and 16s ribosomal DNA sequenc- ing, as well as computational tools that can analyze large data sets. "These techniques have allowed us to explore and characterize these microbial communities and begin to determine their relationship and contribution to overall health," Dr. Park said. The earliest studies in the human microbiome have related to gut health, and Dr. Park cited the treatment of Pseudomembranous colitis with fecal microbiota trans- plantation as a success in this area. "This is a clinical procedure that in- troduces stool from a healthy donor via colonoscopy or enema to restore healthy gut microbiota and combat potentially fatal Clostridium difficile infections," she said. Among the general population, a better understanding of the gut microbiome has led to the use of oral probiotic supplements or the consumption of probiotic-rich foods to return the gut to a healthy state, such as after antibiotic use for an in- fection. "There is still not conclusive evidence to how and when probi- otics should be applied for newer applications," Dr. Wang said. "We still do not know what strains are best for specific conditions. The lack of knowledge is a drawback for rec- ommending their widespread use." Still, they are generally thought of as safe except for minor side effects like gas and bloating. Honing in on the eye How does this background on the human microbiome set the stage for an ocular microbiome? "Further investigation of the ocular surface microbiome, as well as the microbiome of other areas of the body such as the oral mucosa and gut, and their role in the pathophys- iology of diseases is a significant, emerging field of research, and may someday enable the development of novel probiotic approaches for Early findings point to possible role of microbiota in eye disease K nowledge from the 2008 Human Microbiome Proj- ect has led to numerous clinical insights on the body's microbial species and new treatments for systemic dis- eases. Yet have insights on microbial species helped improve care for eye diseases? It's early along the research pathway to say for sure, but the potential appears promising. Human microbiome and systemic disease Insights from the human microbi- ome and the trillions of bacteria, vi- ruses, and fungi that are part of the human microbiota enhance under- standing of various human diseases and their pathophysiologies, wrote Louise Lu and Ji Liu in "Human mi- crobiota and ophthalmic disease." 1 "Discovery of various aspects of the human microbiota and its role in pathophysiology and pathogenesis has revolutionized our approach in studying certain diseases and devel- oping novel treatment modalities," they wrote. The research in this area has led to specific systemic disease insights. "Evidence has indicated that altered gut microbiome can contribute to bowel disease, such as inflammatory bowel disease; autoimmune condi- tions, glycemic control related to diabetes, lipid metabolism related to cholesterol; and pain sensitization, which may be related to depression and anxiety, among other condi- tions," said Ming Wang, MD, PhD, Wang Vision 3D Cataract & LASIK Center, Nashville, Tennessee. "What has occurred in the last decade is the advent of culture-inde- pendent techniques to identify and quantify microbes in these complex communities," said Lisa Park, MD, associate professor of ophthalmol- ogy, Columbia University Medical Center, New York. This includes the Human microbiome research makes headway but ocular microbiome research still emerging

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