Differential gut microbiome profiles in diabetic retinopathy: A comparative study across continental populations

Gut dysbiosis damages gut barrier, stimulates inflammation, endotoxemia, and breakdown of blood-retina barrier, promoting diabetic retinopathy (DR). Most microbiome studies on DR relied on 16S rRNA gene sequencing, documenting altered microbial richness, diversity, and shifts in dominant phyla and genera, though these findings remain inconsistent across populations. The only shotgun metagenomic study to date identified species Eubacterium hallii, Firmicutes bacterium and Alistipes finegoldii enriched in DR, with altered metabolic pathways. The β-diversity showed distinct inter-individual variations in diseased individuals compared to healthy controls (HC). The objective of this narrative review is to highlight the key microbial biomarkers, metabolic pathways, and putative microbiota-gut-retina axis integrating both 16S rRNA and shotgun data to compare microbial alterations across HC, T2DM, and DR. The review concludes with a comprehensive understanding of dysbiotic gut taxa associated with DM and DR in different populations showing wide variability in results mostly due to small sample size, geography, antidiabetic medications, lack of demographic and clinical data and limited taxonomic classification by 16S sequencing. This emphasizes the need of a large scale, multi-ethnic shotgun metagenomic sequencing study with systematically collected medical data and dietary information to understand the contributions of gut microbiome in the progression of DR.