28 May 2019

The gut – eye axis: can our intestines influence our eye health?

Our Director of Research, Mike Bowen, looks at the correlation between gut health and eye health.

Over the last 10-15 years there has been increasing interest in and evidence relating to the relationships between the bacteria that colonise our bodies, and our general health. 

Research has begun to suggest links between the state of our microbiota (the term used to describe these colonies of bacteria living in and on us) and specific diseases and conditions, such as obesity1, depression2, type 1 diabetes3, type 2 diabetes4 and inflammatory bowel disease5. Such studies have found that people with these conditions have lower diversity in their microbiotas. 

You may well have seen news stories about faecal transplants6 being used to treat persistent Clostridium difficile infections – this is now routine practice around the world in response to persistent Clostridium difficile infections. Gut microbes have also been found to play roles in mediating tumour growth, immune system functions, metabolic efficiency and a range of neurological and developmental health issues as well.

At present we know far less than we need to know. But the emerging evidence points to far more complex links between the health of our guts and that of our eyes. What we eat may affect our eye health in far more subtle and intricate ways than we previously thought. ARVO 2019 provided a session dedicated to the research in this area, so vision and eye health researchers and clinician scientists are beginning to pay serious attention to the possibility that gut health may = healthy eyes?

"The emerging evidence points to far more complex links between the health of our guts and that of our eyes"

What does the health of the bacterial colonies in our bodies have to do with the health of our eyes? Migration of microbes7 from one part of the body to another area or areas, whether due to leaky intestinal membranes, or other circulatory / lymphatic routes, has been found to occur far more often than previously thought. However, received wisdom has been that the eyes are immune privileged in some interesting and unusual ways, so surely this would protect them from the transmigration of microbes? 

Apparently not, as research in mice has found that autoimmune uveitis can be caused by T cells (a type of lymphocyte which develops in the thymus that plays a central role in the immune response) that have been activated by gut bacteria8 to target retinal proteins. Once activated these T cells travel through the circulatory system to the eye, where they cause the autoimmune response leading to uveitis. Other research9 has shown that the surface of our eyes has its own bacterial ecosystem, requiring further investigation.

It seems likely that we will see more research in the areas of the ocular microbial ecosystem, and the interactions between eye health our microbial flora and fauna systemically.
 

References

1 Turnbaugh PJ, Hamady M, Yatsunenko T, et al. “A core gut microbiome in obese and lean twins.” Nature2009;457:480-4. doi:10.1038/nature07540 pmid:19043404 CrossRef PubMed, Web of Science, Google Scholar

2 Editorial. “Links between gut microbes and depression strengthened.” Nature. 2019.

3 de Goffau MC, Luopajärvi K, Knip M, et al. “Fecal microbiota composition differs between children with β-cell autoimmunity and those without.” Diabetes 2013;62:1238-44. doi:10.2337/db12-0526 pmid:23274889 Abstract/FREE Full Text, Google Scholar

4 Lambeth SM, Carson T, Lowe J, et al. “Composition, diversity and abundance of gut microbiome in prediabetes and type 2 diabetes.” J Diabetes Obes2015;2:1-7.pmid:26756039 PubMed, Google Scholar

5 Manichanh C, Rigottier-Gois L, Bonnaud E, et al. “Reduced diversity of faecal microbiota in Crohn’s disease revealed by a metagenomic approach.” Gut 2006;55:205-11. doi:10.1136/gut.2005.073817 pmid:16188921 Abstract/FREE Full Text, Google Scholar

6 DeFilipp Z, Peled JU, Li S, et al. “Third-party fecal microbiota transplantation following allo-HCT reconstitutes microbiome diversity.” Blood Adv2018;2:745-53. doi:10.1182/bloodadvances.2018017731 pmid:29592876
Google Scholar

7 Cerajewska, T. L. Davies, M. West, N. X. “Periodontitis: a potential risk factor for Alzheimer disease” BDJ 2016/04/01/online British Dental Association  

8 Horai, Zarate-Blades et al. “Microbiota-dependent activation of an autoreactive T cell receptor provokes autoimmunity in an immunologically privileged site.” Immunity,

9 Cavuoto KM, Banerjee S, Miller D, Galor A. “Composition and Comparison of the Ocular Surface Microbiome in Infants and Older Children.” Transl Vis Sci Technol. 2018;7(6):16. Published 2018 Nov 30. doi:10.1167/tvst.7.6.16

Related further reading

Here we summarise three research papers from a recent issue of Optometry in Practice.

Here we summarise three research papers from a recent issue of Optometry in Practice.

Kathy Oxtoby looks at what qualitative research adds to clinical evidence and how it provides human insights that can’t be measured in numbers.