Abstract
Recent studies have highlighted the association between ocular diseases and microbiota profiles of the host intestinal tract and oral cavity. There is mounting evidence supporting the existence of a ‘gut–eye axis’, whereby changes in gut microbiome alter host immunity, with consequential implications for ocular health and disease. In this review, we examined recent published findings on the association between gut microbiome and ocular morbidity, based on 25 original articles published between 2011 to 2020. The review included both clinical and in vivo animal studies, with particular focus on the influence of the microbiome on host immunity and metabolism. Significant associations between altered intestinal microbiome and specific ocular diseases and pathological processes, including Behçet’s syndrome, autoimmune uveitis, age-related macular degeneration, choroidal neovascularization, bacterial keratitis, and Sjögren-like lacrimal keratoconjunctivitis have been demonstrated. Furthermore, alterations in the gut microbiome resulted in quantifiable changes in the host immune response, suggesting immunopathogenesis as the basis for the link between intestinal dysbiosis and ocular disease. We also examined and compared different techniques used in the identification and quantification of gut microorganisms. With our enhanced understanding of the potential role of gut commensals in ophthalmic disease, the stage is set for further studies on the underlying mechanisms linking the gut microbiome, the host immune response, and the pathogenesis of ophthalmic disease.
Highlights
The results suggest that peripheral bacterial activity and/or products may potentially have a role in glaucomatous optic neuropathy progression, as indicated by the finding of more prominent neurodegeneration and microglia activation of the retina and optic nerve with excessive bacterial loads
There is mounting evidence to support the important role of the gut microbiome in the pathogenesis of ophthalmic diseases, suggesting it is a promising target for both preventive measures and therapeutic treatments
An increasing number of studies have demonstrated that disruptions in gut microbiota impacted host immunity, as evidenced by altered T and B cell responses and cytokine secretion, as well as host metabolic responses
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Therapeutic strategies targeting the intestinal microbiome are promising alternative methods to conventional treatments for ocular inflammatory diseases [1]. Such treatments include the use of antibiotics, introduction of specific microbes, use of probiotics, and fecal transplant therapy [2]. A clear association between ophthalmic inflammatory disease and the intestinal microbiome is illustrated by the relationship between acute anterior uveitis and specific spondylarthritis subtypes; ankylosing spondylitis, reactive. Only original articles were included, excluding review papers papers and meta-analyses. This produced a list of 18 relevant articles (see Figure 1). Reduction in interleukin-13 and interleukin-13/Interferon-γ ratios and reduction in expression of the natural killer (NK)/natural killer T(NKT)
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