An Update and Overview of the Ocular and Extraocular Microbiome and Its Impact on Ophthalmic Care

The microbiome has been described as the last human "organ" and is currently the topic of great research interest worldwide. The application of culture-independent methods, like 16S ribosomal next-generation sequencing, has offered researchers the opportunity to identify bacterial populations that were impossible to detect previously using conventional culture methods. Further standardization of these new approaches to characterizing the microbiome is desirable. The present review discusses the mounting evidence suggesting that alterations in the microbiome and microbial metabolites, such as short-chain fatty acids in the gut, mouth, and ocular surface, may play a key role in the pathogenesis of ocular pathologies such as ocular surface disease, glaucoma, uveitis, age-related macular degeneration, and diabetic retinopathy. Clarifying the probable role of the microbiome in ocular diseases would not only offer valuable insights into pathogenesis but could also enable the development of novel therapeutic approaches. As yet, microbial-based therapeutic applications in ophthalmology are limited. Nevertheless, recently emerging strategies utilizing probiotics and prebiotics, or even fecal transplantation to regulate microbiome composition, offer promising research avenues for developing future innovative therapies for ocular diseases. Further studies employing standardized methodological protocols are needed to ensure the reproducibility of results and to eventually unlock the precise links between the microbiome and the eye.