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Prophylactic antibiotics reduced infection risk after cataract surgery
Subconjunctival antibiotic injections significantly decreased the incidence of endophthalmitis in a study.
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SASKATOON, Canada — The routine use of subconjunctival antibiotic prophylaxis after cataract surgery is under scrutiny due to reports of retinal toxicity. However, a new retrospective study by Kevin Colleaux, MD, and W. Keith Hamilton, MD, suggests that subconjunctival antibiotic injections following cataract surgery significantly decrease the incidence of postoperative endophthalmitis.
“Hopefully, more surgeons will consider and use this technique to reduce or eliminate endophthalmitis as a potentially devastating complication of modern cataract surgery,” said Dr. Hamilton, an associate professor of ophthalmology at the University of Saskatchewan here.
“I have never had a case of endophthalmitis in 11 years of a busy cataract surgery practice with this technique,” he said.
The development of resistant bacterial strains as a result of indiscriminate use of antibiotics has prompted a re-examination of prophylaxis in the medical world; ocular surgery is no exception. There has also been a reported risk of toxic retinal effects with subconjunctival antibiotic injections. However, previous research has suggested that these toxic effects may be due to inadvertent intraocular injection through the cataract incision of antibiotic in sufficient amounts to be toxic.
The study
Drs. Hamilton and Colleaux examined chart reviews and surgeon surveys from 13,886 consecutive cataract operations performed by nine surgeons between September 1, 1994, and January 31, 1998, at the Saskatoon City Hospital. All the cataract extractions were by phacoemulsification and were performed at the same hospital-based surgical unit in Saskatoon. The incidence of postoperative endophthalmitis was assessed in patients receiving preoperative antibiotic drops and subconjunctival antibiotic injections at the conclusion of surgery. Subconjunctival antibiotics used were gentamycin, cetazolin or both.
The study, published in the Canadian Journal of Ophthalmology, also examined the type of incision (clear-corneal versus scleral tunnel) used for cataract surgery and the incidence of infection. The antibiotic drops used over the course of the study included tobramycin, gentamicin, ofloxacin and polymyxin-trimethoprim. Patients who received the drops for several days prior to surgery and only on the day of surgery were analyzed as one group.
Among the 13,886 procedures, only 10 cases of endophthalmitis were reported. The most common infecting organism was Staphylococcus epidermidis (four cases) followed by Pseudomonas aeruginosa, S. aureus, Streptococcus pneumoniae and enterococcus, with one case each.
Patients undergoing clear-corneal surgery without preoperative antibiotic drops or subconjunctival antibiotic injections had the highest incidence of endophthalmitis (0.417%). The postop infection rate was significantly lower with subconjunctival antibiotic injections than without (0.011% versus 0.179%; P=.009). While results showed that use of antibiotic drops lowered the infection rate, the difference was not statistically significant (P=.48). However, the subgroup analysis revealed patients who underwent clear-corneal surgery fared better with the drops than without (0% versus 0.417%).
The researchers concluded that scleral tunnel incisions have a lower rate of infection than clear-corneal incisions, although the difference was not statistically significant (P=.14). However, Drs. Colleaux and Hamilton recommend a self-sealing clear corneal incision to reduce the chances of the antibiotic gaining access to the retina — and creating toxic effects — through the incision itself.
More rigorous study needed
Robert Snyder, MD, head of the Department of Ophthalmology at the University of Arizona, noted that a prospective, controlled trial would give more complete data. However, he conceded that because the postop infection rate is so low, such a study would be costly and difficult to perform.
“A retrospective study has limited power to prove the efficacy of antibiotics,” he said. “This is because of the uncontrolled variables.” Although a proponent of prophylactic antibiotic use himself, Dr. Snyder noted that, given the cost of some drugs, is is also important to determine which antibiotics are most effective. He also said a more rigorous study could clearly determine whether the adverse events associated with an accidental intraocular injection of aminoglycoside — which can include blindness — outweigh the putative benefit of the procedure.
For Your Information:Reference:
- W. Keith Hamilton, MD, can be reached at No. 208, 750 Spadina Cresent East, Saskatoon, SA, S7K 3H3, Canada; +(1) 306-242-9990; fax: +(1) 306-244-1909; e-mail: wkhamilton@home.com.
- Robert W. Snyder, MD, can be reached at 1801 North Campbell Ave., Tucson, AZ, 85719 U.S.A.; +(1) 520-321-3677; fax: +(1) 520-321-3665; e-mail: rsnyder@eyes.arizona.edu.
- Colleaux K, Hamilton WK. Effect of prophylactic antibiotics and incision types on the incidence of endophthalmitis after cataract surgery. Canadian Journal of Ophthalmology. 2000;35(7):373-378.