The Gut-Eye Axis and Microbiome in Ophthalmic Diseases: A Narrative Review.

The gut microbiome regulates host metabolism, barrier integrity, and immune homeostasis through microbe-host signaling and bioactive metabolites. Growing evidence suggests that dysbiosis may also influence ocular immune privilege and blood-retinal barrier stability, supporting the emerging concept of the gut-eye axis. This narrative review aimed to integrate retinal, uveal, and ocular surface disorders within a shared functional framework, with emphasis on recurring mechanistic pathways and their translational relevance rather than on single diseases or isolated taxonomic findings. The review was based on a literature search of PubMed and Scopus and primarily included English-language studies published between 2015 and 2025, with earlier seminal papers included when needed. The search was last updated in March 2026, and 101 sources were included in the final narrative synthesis. Across age-related macular degeneration, diabetic retinopathy, glaucoma, uveitis, dry eye disease, and Sjögren's syndrome, the most consistent microbiome-related signals were functional rather than taxonomic. Recurrent mechanistic themes included Th17/Treg immune programming, barrier dysfunction with microbial product translocation, and systemic metabolite signaling, particularly involving short-chain fatty acids, bile acid receptor pathways, and tryptophan-derived metabolites. Age-related macular degeneration and diabetic retinopathy showed the strongest multi-layered support, whereas uveitis provided a compelling immune-centered biological model that remains limited by treatment-related confounding in human studies. In glaucoma and ocular surface disease, evidence supports biological plausibility, especially in relation to neuroinflammation, mucosal immune dysregulation, and metabolite-dependent anti-inflammatory pathways, although much of the available human literature remains associative. Overall, current evidence supports dysbiosis as a disease modifier that may influence ocular inflammation, angiogenesis, neurodegeneration, and barrier stability. However, clinical translation remains limited by cohort heterogeneity, methodological variability, and incomplete control of confounding factors. Further progress will depend on longitudinal multi-omics cohorts and controlled intervention trials focused on actionable microbial functions.