Jampel HD, Quigley HA, Kerrigan-Baumrind LA, et al. Risk factors for late-onset infection following glaucoma filtration surgery. Arch Ophthalmol 2001;119:1001–1008.
Original study reprint requests: Henry D. Jampel, MD, MHS, Wilmer Eye Institute, Maumenee B-110, 600 N. Wolfe Street, Baltimore, MD 21287–9205.
To determine the risk factors for late-onset infection after glaucoma filtration surgery.
A case-controlled comparison study.
Multiple centers on behalf of the Glaucoma Surgical Study Group.
Supported in part by the Glaucoma Research Foundation, San Francisco, CA.
We performed a case-control study comparing 131 cases of late-onset infection collected from 27 surgeons at 10 centers with 500 controls matched for date of surgery and surgeon. The criterion for the presence of infection was severe anterior chamber reaction occurring later than 4 weeks after surgery. An opaque bleb and positive culture results were not required for diagnosis. Risk factors were identified by univariate and multivariate logistic regression analyses.
Clinical evidence of anterior chamber reaction.
Some of the risk factors that were statistically significant in the multivariate model after adjusting for age, race, and sex were (i) performance of a full-thickness rather than a guarded procedure (risk ratio [RR], 13.1; 95% CI, 2.12–80.9); (ii) filtration surgery performed without concurrent cataract surgery (RR, 2.25; 95% CI, 1.24–4.08), (iii) use of mitomycin (RR, 2.48; 95% CI, 1.06–5.83), (iv) intermittent use of antibiotics after surgery (RR, 2.10; 95% CI, 1.09–4.02), and (v) continuous use of antibiotics after surgery (RR, 5.94; 95% CI, 2.09–16.9).
Eyes undergoing full-thickness procedures or filtration surgery without cataract extraction are at increased risk of late infection. Intraoperative mitomycin and episodic or continuous antibiotic use after the postoperative period are associated with an increased risk of infection.
Endophthalmitis is the most serious late complication of glaucoma filtering surgery. Fortunately, it has a relatively low (although possibly rising) incidence. The infrequency with which it occurs, however, also works against us in collecting meaningful information in case–control studies regarding prevention and management of the complication. Jampel and co-workers sought to overcome this problem by designing a multi-center study with a sufficient number of cases and controls to allow statistically significant associations between risk factors and late-onset infection after glaucoma filtering surgery.
As the authors note, their study design has certain limitations. The retrospective design requires surgeons to recall cases of endophthalmitis, so that some cases from the various centers may not have been included. With 27 surgeons from 10 centers, there may have been inconsistency in case selection, because an opaque bleb and positive culture were not required for the diagnosis. It is also important to note that the results, using linear regression analysis, do not tell us whether there is a cause-and-effect relationship between outcomes and risk factors, but only that they are statistically related. Nevertheless, by using appropriate statistical analyses, the authors were able to provide some clinically useful information from their data.
The authors used multivariate and univariate logistic regression analyses to identify risk factors. Multivariate analyses are critical because, as the authors point out, they adjust for the presence of many related variables. However, there is the risk of one variable being missed if it is closely associated with another variable. For example, the use of mitomycin was not significantly associated with infection, although prior surgery was, but the former did become significant when the latter was removed from the model. It may also identify risk factors that are only indirectly related to the outcome. For example, the absence of concurrent cataract surgery, which was identified as a risk factor, obviously does not mean that pseudophakia protects against endophthalmitis per se, but that the filtering blebs in these eyes tend to be lower and thicker.
Univariate analysis was used to advantage in the present study to identify risk factors that were too incompletely or infrequently recorded in the medical records to be included in the multivariate analyses. This approach led to the identification of inferiorly located blebs, high blebs, bleb leak, and blepharitis as being associated with the development of infection. The clinician, therefore, must be aware of factors such as full-thickness procedures, use of mitomycin, and intermittent or chronic use of antibiotics to identify patients at higher risk of late-onset infection, but must also pay close attention to the bleb appearance and related ocular findings to anticipate and hopefully prevent the serious consequences of endophthalmitis after glaucoma filtering surgery.