Oral Intake of Streptococcus thermophilus iHA318 Mitigates Dry Eye Symptoms in a Randomized Clinical Study

Background/Objectives: A probiotic Streptococcus thermophilus (iHA318) has been demonstrated to alleviate dry eye symptoms in a mouse model. This study investigated its effects on dry eye mitigation in a clinical trial. Methods: A total of 68 volunteers were recruited in the double-blind clinical trial and randomly divided into a probiotic group and a placebo group. The probiotic group received iHA318 capsules daily for 35 days via oral intake, while the placebo group received microcrystalline cellulose capsules. Assessments before and after the intervention were performed for the tear volume (TV), tear break-up time (TBUT), tear osmolarity (Osmo), serum sialic acid (SA) concentrations, and the Ocular Surface Disease Index (OSDI), and an impression cytology analysis was conducted for immunofluorescence detection of NLRP3 expression. Results: The tear volume was significantly increased in the probiotic group, although a placebo effect was observed in the placebo group. The probiotic group showed a significant reduction in tear osmolarity, an extended TBUT, and an improved OSDI score. These parameters were also observed in the placebo group without statistical significance. In addition, the serum SA was significantly increased in the probiotic group in contrast to a slight non-significant increase in the placebo group. Reductions in NLRP3 inflammasome activation and OSDI were found only in the probiotic group. Conclusions: In conclusion, a significant improvement in major dry eye symptoms after iHA318 treatment was observed compared to the placebo group.