OBJECTIVES: To profile the array of microbial contaminants of eye drops, both native and non-native to the ocular surface, and associated factors for contamination. METHODS: Potentially relevant studies were retrieved from major bibliographic databases (PubMed, Scopus, and Web of Science). Data were extracted, and study-specific estimates of the contamination rates of topical ophthalmic solutions were combined using meta-analysis to obtain pooled results. RESULTS: A total of 33 studies that evaluated the microbial contamination rate in 4600 samples were included in this study. The microbial contamination rate of in-use ophthalmic medications is 10% (95% CI: 6%-17%
PI: 0%-78%, I2=95.1%). The contamination rate among diagnostic eye drops is 13% (95% CI: 3%-42%
PI: 0%-98%, I2=95.6%), and the contamination rate among therapeutic eye drops is 10% (95% CI: 6%-17%
PI: 1%-63%, I2=94.9%). Staphylococcus spp. were the most prevalent gram-positive bacterial contaminants [3.55% (95% CI: 1.52%-8.04%
PI: 0.08%-63.46%), I2=93.2%], Escherichia coli, the most prevalent gram-negative contaminants [1.02% (95% CI: 0.50%-2.05%
PI: 0.16 to 6.04%), I2=24.8%], and Aspergillus spp., the most prevalent fungal contaminants [0.88% (95% CI: 0.31%-2.51%
PI: 0.03%-22.05%), I2=89.9%]. CONCLUSION: There is a high rate of microbial contamination in topical ophthalmic solutions, which has implications for patient safety and the effort to stem avoidable blindness. Similar to injectable medications, we recommend using single-use vials for topical ophthalmic solutions, as opposed to multi-use vials, which are stored for a protracted period of time and used on multiple patients.