Preventing endophthalmitis: can we reach a consensus?

May 1, 2007

Assessing povidone-iodine as method for preventing endophthalmitis.

Identifying the source

The bacteria for this infection are thought to come from three main sources:1
1. Patients' conjunctival flora.
2. Surgeons and surgical team contamination.
3. Surgical equipment contamination.

Meticulous scrubbing of staff and good sterilization of both the equipment and surgical field can help to control the latter two sources but it is the patient's own flora that is thought to be the most common source of the infection.

Once clinical infection occurs, damage to ocular tissues is believed to be caused by the direct effects of bacterial replication as well as initiation of a fulminant cascade of inflammatory mediators. Endotoxins and other bacterial products appear to cause direct cellular injury while eliciting cytokines that attract neutrophils, which enhance the inflammatory effect. Recent work at controlling the damaging effects of endophthalmitis have focused not only on identifying appropriate antibiotics for control of the infectious agent but also on anti-inflammatory agents that might disrupt the immunologic events that occur after infection.3, 4, 5

We recently conducted a clinical study to compare the efficacy of using 0.5% chloramphenicol eye drops with 5% povidone-iodine drops in the conjunctival sac to reduce the number of viable colonies of bacteria isolated from the conjunctiva of patients undergoing phacoemulsification cataract surgery. Povidone-iodine is a solution of polyvinylpyrrolidone and iodine used as an antibacterial.

Putting povidone iodine to the test

We enrolled 100 patients, undergoing phacoemulsification in one eye under topical anaesthesia, to take part in the study. Each patient was admitted to the day case centre on the day of surgery and received topical medications for pupil dilation consisting of 1% tropicamide, 2.5% phenylephrine; and topical medications for anaesthesia in the form of 0.5% bupivacain. All medications were given three times in the operation eye.

On arrival at theatre, the patient was positioned on the operating table and a swab from both the operation eye [study eye; swab A] and from the non-operation eye [control eye; swab B] was obtained by the surgeon. The periorbital skin of the study eye was cleaned carefully with povidone-iodine solution, ensuring that it did not get into the patient's eye. Two drops of 0.5% chloramphenicol (Chauvin Pharmaceuticals Ltd.) were applied into the control eye and two drops of 5% povidone-iodine (Medlock Medical Ltd.) were used in the study eye. The operation was then conducted as usual. Swab C was taken from the conjunctiva of the study eye, and swab D was taken from the conjunctiva of the control eye before giving the sub-conjunctival injection in the operation eye.

Although the surgeon was not masked to the swabs, the microbiologist analysing these swabs was masked to all of them. The samples, obtained using sterile cotton-based conjunctival bacterial swabs, were sent straight to the microbiology lab for culture on blood agar and chocolate agar solid plates. Plates were incubated for 48 hours at 37° C.

Colony Forming Units (CFU) were counted and the results were examined using Analysis of Variance between groups (ANOVA) one way analysis with Mann Whitney test. The P-value was calculated; p<0.05 was considered as statistically significant.