Prospective evaluation of external ocular microbial growth and aqueous humor contamination during cataract surgery

Purpose: To analyze the route oi aqueous humor contamination leading to the development of postoperative endophthalmitis. Setting: Department oi Ophthalmology, University of Helsinki, Finland. Methods: Forty-nine eyes of 49 patients (31 having phacoemulsification and 18 extracapsular cataract extraction [ECCE]) participated in the study. Fou r bacterial cultures were taken: preoperative conjunctival swab, lid margin culture, intraoperative lacrimal lake sample, and immediate postoperative anterior chamber fluid sample, Results: Preoperative lid margin cultures were positive in 59.2% of eyes, c onjunctival cultures in 69.4%, and lacrimal lake cultures in 24.9%. Four aq ueous humor samples (8.2%) showed bacterial growth in the anterior chamber aspirate: 3 in the phacoemulsification and 1 in the ECCE group. The bacteri a isolated in this study, Staphylococcus epidermidis and Propionibacterium acnes (2 positive isolates each) were sensitive to the preoperative topical antibiotics used. No aqueous humor sample or any from other locations show ed gram-negative microbe growth. The most frequently recovered microbes in all samples collected from the 3 other sources were S epidermidis and other coagulase-negative staphylococcus species, followed by P acnes and other p ropionibacterium species, Staphylococcus aureus, and diptheroids. Conclusion: The ocular surface significantly contributed to the transmissio n oi microbes into the eye during cataract surgery. These microbes could no t be eradicated by topical preoperative antibiotics. However, no patient de veloped postoperative endophthalmitis. Natural defense mechanisms appear to lend off a minor inoculum with these microbes of relatively low pathogenic ity.