Abstract
The gut microbiome has been found to influence diseases of the gastrointestinal tract as well as diseases in remote sites such as the brain, lung, and eye. As such, gut microbiome manipulation has been explored as a treatment for several diseases including, Clostridium difficile infection, inflammatory bowel disease (IBD), and rheumatic diseases. Microbiome manipulation techniques include dietary changes, pre and probiotics, and fecal microbiota transplantation (FMT). Some dietary changes in IBD, including gluten-free and vegetarian diets, were shown to change the gut microbiome (e.g., genera Bacteroides, Faecalibacterium, Blautia) but had a limited effect on clinical outcomes (e.g., surgical complication, fistula formation, hospitalization). While other diets, such as low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet and high adherence to a Mediterranean diet, were shown to improve IBD and rheumatoid arthritis disease activity (e.g., stool frequency, joint tenderness), as well as change the gut microbiome (e.g., F. pransnitzii spp, Blautia). Pre and probiotic therapies have had more promising results, especially in IBD, with significant improvements in disease activity, intestinal permeability, and endoscopic findings following the intervention. Lastly, while FMT has been most frequently studied as a treatment for C. difficile infection, it has also been applied to immune diseases (e.g., ulcerative colitis, graft vs. host disease (GVHD), immune-mediated dry eye), with the goal of transplanting beneficial bacteria (e.g., Blautia, Faecalibacterium, and Bacteroides) from a healthy donor. Finally, probiotics have also been delivered to locations outside the gut, with Lactobacillus eye drops investigated for vernal keratoconjunctivitis. This chapter discusses how microbiome manipulations (gut and eye) have been used to modulate clinical outcomes of diseases that have relevance to the eye (e.g., autoimmune diseases) and discusses how these strategies may be applied in the future to the treatment of eye diseases in which microbiome abnormalities have been implicated (e.g., uveitis, dry eye, diabetic retinopathy).