Living with your biome: how the bacterial microbiome impacts ocular surface health and disease

ABSTRACT

Introduction

Microbiome research has grown exponentially, but the ocular surface microbiome (OSM) remains an area in need of further study. This review aims to explore its complexity, disease-related microbial changes, and immune interactions, and highlights the potential for its manipulation as a therapeutic for ocular surface diseases.

Areas Covered

We introduce the OSM by location and describe what constitutes a normal OSM. Second, we highlight aspects of the ocular immune system and discuss potential immune microbiome interactions in health and disease. Finally, we highlight how microbiome manipulation may have therapeutic potential for ocular surface diseases.

Expert Opinion

The ocular surface microbiome varies across its different regions, with core phyla identified, but with genus variability. A few studies have linked microbiome composition to diseases like dry eye, but more research is needed, including examining microbiome interactions with the host. Studies have noted that manipulating the microbiome may impact disease presentation. As such, microbiome manipulation via diet, oral, and topical pre- and probiotics, and hygienic measures may provide new therapeutic algorithms in ocular surface diseases.

KEYWORDS:

• Ocular surface microbiome
• immune system of the ocular surface
• osm modulation
• dry eye disease
• MIcrobiome Directed Therapies

Article highlights

• The composition of the normal ocular surface microbiome (OSM) varies by ocular site, with a relatively pauci-bacterial cornea contrasted with a higher bacterial burden found within the conjunctiva and eyelid.

• The composition of the OSM may change with disease, including with dry eye, among other conditions.

• The natural immune system of the ocular surface relies heavily on a barrier function as well as intricate cell-mediated processes orchestrated by dendritic cells, macrophages and lymphocytes that interact with commensal bacteria.

• Ocular commensal bacteria may stimulate the inflammasome to produce IL-1β, which can further exacerbate inflammation in autoinflammatory syndromes.

• While techniques such as fecal microbiota transplant have yet to prove therapeutic in ocular surface disease, manipulation of the microbiome through diet, pro-biotics, topical therapy, and other medications may be a future therapeutic avenue.

Declaration of financial/other relationships

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was supported by the National Eye Institute U24EY035102 (awarded to A. Galor and A. St. Leger); the Department of Veterans Affairs, Veterans Health Administration, Office of Research and DeveFlopment, Clinical Sciences R&D (CSRD) I01 CX002015 (awarded to A. Galor), Biomedical Laboratory R&D (BLRD) Service I01 BX004893 (awarded to A. Galor), Rehabilitation R&D (RRD) I21 RX003883 (awarded to A. Galor), Department of Defense Gulf War Illness Research Program (GWIRP) W81XWH-20-1-0579 (awarded to A. Galor) and Vision Research Program (VRP) W81XWH-20-1-0820 (awarded to A. Galor), National Eye Institute U01 EY034686 (awarded to A. Galor), R33EY032468 (awarded to A. Galor), NIH Center Core Grant P30EY014801 (Institutional), U01EY034711 (awarded to A. St. Leger), R01EY032482 (awarded to A. St. Leger), R01EY026891 (awarded to A. St. Leger), P30EY008098 (Institutional Pitt). Both Miami and the University of Pittsburgh have Research to Prevent Blindness Unrestricted Grants GR004596-1 (institutional), and The Eye and Ear Foundation of Pittsburgh.