|
THE occurrence of post-cataract surgery endophthalmitis appears to have increased over the past decade, and that trend may be related to the introduction and growth in the use of clear corneal incisions, according to the findings of a meta-analysis undertaken by researchers at the University of California-Irvine. Speaking at the annual meeting of the American Academy of Ophthalmology, Mehran Taban MD presented the results of an exhaustive review of the English language literature that spanned the period January 1963 to March 2003. The review included 215 papers reporting on more than three million cases of cataract surgeries along with 66 studies on penetrating keratoplasty (PK), representing over 90,000 PKs. The PK papers were analysed as a control based on the assumption that any temporal changes in infection rates associated with PK would reflect the evolution of surgical prophylaxis in general since the technique for PK has not changed dramatically over this period. Studies were identified for potential inclusion in the meta-analysis based on the results of a PubMed literature search, manual searching of reference lists, and thorough review of major ophthalmology texts as well as published proceedings and scientific sessions from key meetings. The initial search identified nearly 5,000 cataract surgery papers and nearly 1,900 reports on PK, of which a selected proportion were evaluated fully to identify those that fulfilled the study's inclusion criteria. During the entire study period, the rate of endophthalmitis was about three-fold higher for PK compared with cataract surgery, 0.38% vs. 0.13%, respectively. The researchers compared the data from studies before and after 1992, the year Howard Fine MD introduced the clear corneal incision. The investigators also looked at the data before and after January 2000, which according to ASCRS survey data was the year the clear corneal incision technique approached majority use by cataract surgeons. The analysis showed a correlation between the increased use of clear corneal incisions and an increased incidence of endophthalmitis after cataract surgery. The correlation was evident both qualitatively, using a weighted linear regression analysis and determination of the slope coefficient of plots of infection rates over time, as well as quantitatively, based on a relative risk comparison of pooled estimates of endophthalmitis rates between study periods and of different cataract incision techniques. The rates of post-cataract surgery endophthalmitis showed a gradual downward trend between 1963 and 1991. However, that trend was reversed from 1992-2003. In contrast, the opposite pattern was seen in the slope coefficients for the graphs of post-PK endophthalmitis rates over time. For the period from 2000-2003, the rate of endophthalmitis after cataract surgery was 0.27%, representing almost a 2.5-fold increase relative to that calculated for the earlier time interval (1963-1999). The post-PK rate approached 0.2% during 2000-2003, which was about half of what it had been in the pooled estimate for previous years. Considering cataract surgery data only for the years 1992-2003, clear corneal incision was associated with an approximate 2.5-fold increased risk of endophthalmitis compared with scleral incision and more than a threefold increase versus limbal incision. Those differences were statistically significant. There was no significant difference in the rate of endophthalmitis after cataract surgery when comparing limbal and scleral incision approaches. "If one considers that in the year 2001, over 2.5 million cataract surgeries were performed in the United States and over 10 million worldwide, the recent increase in endophthalmitis rate would translate to about 4,000 and 16,000 additional cases annually, respectively," said Dr. Taban. He continued, "However, our findings need to be confirmed in further studies as there is inevitable bias resulting from the review of studies submitted or accepted for publication that can potentially affect the results of a meta-analysis. Such bias might be eliminated through comprehensive registration of all initiated clinical trials, or the hypothesis generating this review could be tested in a large-scale, prospective trial with defined inclusion criteria." Dr. Taban noted that various theories have been proposed to explain why clear corneal incision might increase the risk of post-cataract surgery endophthalmitis. Those are based on poorer stability of the surgical wound and the fact that a defect in the clear corneal wound may not be readily apparent intraoperatively. In the discussion of this paper, Terrence P. O'Brien, MD, agreed that recent evidence supports the conclusion that the incidence of endophthalmitis after cataract surgery is on the rise, but that given the limitations of the meta-analysis technique, no conclusions can be drawn on the exact role of the clear corneal incision. Therefore, he agreed with Dr. Taban on the need for further studies and the value of an international collaborative registry of all initiated clinical trials. "Continued vigilance in surveillance of infection is necessary and further confirmation of these findings from a large prospective trial would be welcome," Dr. O'Brien said. Other panel members noted it is plausible that clear cornea incision might increase the risk of endophthalmitis because it is a much less forgiving site for wound construction. However, they proposed that surgeon technique might also be important in determining the potential for a clear cornea approach to increase the risk of endophthalmitis. "It would be interesting to see if the endophthalmitis incidence rate was higher initially but decreased subsequently as cataract surgeons became familiar with the requirements for adequate clear corneal wound construction. However, if that is not a factor, these data are truly a concern considering that more than half of cataract surgeons are using a clear cornea approach," said Stephen H. Johnson, MD.
Mehran Taban MD Terrence P. O'Brien MD Stephen H Johnson MD
|
