I commend Ng et al.1 for contributing a large retrospective population study of endophthalmitis. By analyzing their large database, they have identified certain factors and practices that appear to affect the rate of endophthalmitis. Some of the findings are consistent with well-accepted tenets, such as the efficacy of topical povidone–iodine antiseptic and the increased infection risk with vitreous loss.2 However, I believe their conclusion that subconjunctival antibiotic injection appears to be beneficial for endophthalmitis prophylaxis deserves further discussion and qualification.
In January 2007, the American Society of Cataract and Refractive Surgery (ASCRS) Cataract Clinical Committee conducted an online poll of current endophthalmitis prophylaxis practices to which 1312 members responded. When asked whether antibiotics were administered at the conclusion of surgery, only 11% of the respondents said they used subconjunctival antibiotics. In comparison, 75% used topical antibiotics, 14% used an intracameral injection, 3% used a collagen shield, and 10% did not use antibiotics immediately after surgery. (The percentages total more than 100 because some respondents used multiple methods.) Because most respondents (89%) currently do not use subconjunctival antibiotics, the question of whether they should alter their antibiotic regimen based on this study may arise. I am concerned that statements such as “[w]e found that antibiotic prophylaxis was a significant benefit, but only if given as a subconjunctival injection” may be taken out of context.
Conducting this study required the authors to collect and analyze an enormous amount of data. We always learn valuable information from such diligent efforts. However, we must be cautious about making practice recommendations based solely on retrospective population studies with multiple covariables. Furthermore, this study encompassed a 2-decade-long period during which most surgeons undoubtedly changed their surgical technique several times. This probably multiplies the number of confounding variables that can affect the rate of infection. Finally, in a retrospective study it is very hard to differentiate infectious endophthalmitis from noninfectious inflammation (eg, toxic anterior segment syndrome).
The most intriguing suggestion, of course, is that subconjunctival antibiotics appeared to protect against infectious endophthalmitis. If true, this might partially explain the increase in endophthalmitis rates associated with clear corneal incisions reported in other papers3,4 but not found in this study. For most surgeons, the transition to clear corneal incisions with topical anesthesia meant eliminating the subconjunctival antibiotic injection. Unfortunately, the study cannot properly address the question of whether subconjunctival injection is superior to topical or intracameral delivery of antibiotics. As Ng et al. acknowledge, there was insufficient statistical power to assess the benefit of topical or intracameral antibiotics. This is because most of the surgeons used topical antibiotics and did not use intracameral antibiotics.
Overall, I consider this study to be additional supporting evidence that an intracameral level of antibiotic (immediately postoperatively) is beneficial in preventing infectious endophthalmitis.5 Whether this is achieved by subconjunctival or intracameral injection, with an antibiotic-soaked collagen shield or by topical administration of fluoroquinolones with excellent intraocular penetration, I believe that at least one of these measures should be strongly considered at the conclusion of surgery.
1. Ng JQ, Morlet N, Bulsara MK, Semmens JB. Reducing the risk for endophthalmitis after cataract surgery: population-based nested case-control study; Endophthalmitis Population Study of Western Australia sixth report. J Cataract Refract Surg. 2007;33:269-280.
2. Speaker MG, Menikoff JA. Prophylaxis of endophthalmitis with topical povidone-iodine. Ophthalmology. 1991;98:1769-1775.
3. Cooper BA, Holekamp NM, Bohigian G, Thompson PA. Case-control study of endophthalmitis after cataract surgery comparing scleral tunnel and clear corneal wounds. Am J Ophthalmol. 2003;136:300-305.
4. Taban M, Behrens A, Newcomb RL, et al. Acute endophthalmitis following cataract surgery; a systematic review of the literature. Arch Ophthalmol. 2005;123:613-620.
5. Barry P, Seal DV, Gettinby G, et al. ESCRS study of prophylaxis of postoperative endophthalmitis after cataract surgery; preliminary report of principal results from a European multicenter study; the ESCRS Endophthalmitis Study Group. J Cataract Refract Surg. 2006;32:407-410.