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Abstract
Background Dry eye syndrome (DES) is a multifactorial ocular disorder affecting millions worldwide, with emerging evidence suggesting a connection between gut health and ocular pathology, termed the ‘gut-eye axis’. Probiotics, renowned for their immunomodulatory and anti-inflammatory properties, have emerged as a potential therapeutic approach for DES. This systematic review aimed to evaluate the efficacy of probiotic interventions in alleviating DES symptoms and improving ocular surface parameters.
Methods Based on the PRISMA guidelines, a thorough systematic search of electronic databases (PubMed, Web of Science, Scopus) up till 15 April 2024 identified relevant studies using ‘Probiotic’ AND ‘Dry Eye’ as the MeSH terms. Studies investigating the effects of probiotics on DES and dry eye symptoms in associated diseases were included. Narrative reviews and studies without including the probiotic intervention were excluded.
Results Thirteen studies met the inclusion criteria, comprising randomized controlled trials (RCTs) (n=6) and animal models (n=7). Probiotic interventions were administered via eye drops and oral capsules in human trials, while animal studies utilized oral gavage. Lactobacillus and Bifidobacterium were commonly tested genera in monotherapy or combination forms. Modulation of gut microbiota composition upon probiotic treatment was reported in genetically manipulated autoimmune, environmental-induced and chemical-induced DES animal models with improved clinical manifestation correlating to improved tear secretion, reduced ocular surface inflammation, preserved goblet cell density and corneal barrier function. Additionally, oral probiotic supplementation induced alterations in the lacrimal gland proteome associated with immunomodulation in DES mice. However, clinical trials demonstrated varying results. Two RCTs exhibited improved tear production with probiotic eye drops, while another trial indicated efficacy only with eye drop formulation, not live probiotics in oral capsules. Meanwhile, a recent trial suggested symbiotic (probiotic + prebiotic) supplementation improved tear film stability and Ocular Surface Disease Index (IDDF2024-ABS-0103 Figure 1).
Conclusions In conclusion, probiotic interventions hold promise for alleviating DES symptoms and enhancing ocular surface parameters. However, inconsistencies in clinical trial outcomes underscore the need for further research to optimize formulations and dosages of strain-specific probiotics tailored to specific disease contexts. Personalized treatment strategies may thus be developed, to provide alternative and more effective solutions for managing DES.