Eyeworld

MAR 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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116 EW RESIDENTS March 2012 EyeWorld journal club Duke University residents' review of "Impact of failure of trabeculectomy with mitomycin-C" by Peter C. Nicholas, M.D., Ph.D., Michael J. Allingham, M.D., Ph.D., Mark Hansen, M.D., Laura Vickers, M.D., and Pratap Challa, M.D. Pratap Challa, M.D. Residency program director, Duke University This month, I asked the residents at Duke to review this Japanese paper looking at whether phaco adversely affects the function of a prior trabeculectomy. —David F. Chang, M.D., chief medical editor I n the article published this month in JCRS, "Impact of pha- coemulsification on failure of trabeculectomy with mito- mycin-C," Nanako Awai- Kasoaka et al. attempted to further elucidate the effect of phacoemulsifi- cation on IOP control after tra- beculectomy. To date, published studies report conflicting answers to this question. This retrospective study evaluated phacoemulsification after trabeculectomy with mito- mycin-C (MMC) as a risk factor for subsequent failure of trabeculectomy surgery. The study included 178 pa- tients who had undergone tra- beculectomy with MMC for either primary open-angle glaucoma (POAG) or pseudoexfoliation glau- coma (PXG). Thirty-seven of these patients subsequently underwent phacoemulsification. The primary endpoints were failure of the tra- beculectomy as defined by either: condition A (persistent intraocular pressure [IOP] greater than 21 mm Hg or additional glaucoma proce- dures) or condition B (persistent IOP greater than 18 mm Hg or additional glaucoma procedures). The authors used the Cox proportional hazard model to identify the relative risk of Impact of phacoemulsification on failure of trabeculectomy with mitomycin-C Nanako Awai-Kasaoka, M.D., Toshihiro Inoue, M.D., Ph.D., Yuji Takihara, M.D., Ph.D., Atsushi Kawaguchi, Ph.D., Masaru Inatani, M.D., Ph.D., Minako Ogata-Iwao, M.D., Hidenobu Tanihara, M.D., Ph.D. J Cataract Refract Surg (March) 2012; 38:419-424 Purpose: To evaluate whether phacoemulsification after trabeculectomy affects post-op IOP Setting: Kumamoto University, Kumamoto, Japan Design: Cohort study Methods: The medical records of patients with primary open-angle glaucoma or pseudoexfoliation glaucoma who had trabeculectomy with mitomycin-C were reviewed. The primary endpoints were con- dition A (persistent post-op IOP 21 mm Hg or higher or additional glaucoma procedures with or without medications) and condition B (post-op IOP 18 mm Hg or higher or additional glaucoma procedures with or without medications). Multivariable analysis was performed using the Cox proportional hazards model. Results: The records of 178 patients (178 eyes) were reviewed. The mean follow-up was 37.0 months. For condition A, the probability of treatment success at 1 year, 2 years, and 3 years was 97.9%, 95.0%, and 92.7%, respectively. For condition B, the corresponding probabilities of success were 92.3%, 84.1%, and 81.8%. Thirty-seven patients (37 eyes) had phacoemulsification after trabeculectomy; 10 of those patients had phacoemulsification within 1 year after tra- beculectomy. Multivariate analysis showed that a higher IOP before trabeculectomy was a significant risk factor for condition A and condition B (P=.01 and P=.0006, respectively); phacoemulsification within 1 year after trabeculectomy was significantly associated with trabeculectomy failure for condition B (P=.04). Conclusion: Post-op IOP in eyes with previous trabeculectomy may be affected by the IOP before trabeculectomy and phacoemulsifica- tion within 1 year after trabeculectomy. trabeculectomy failure following phacoemulsification cataract surgery. The authors found the 3-year probability of treatment success for all patients who underwent tra- beculectomy with MMC to be 92.7% for condition A and 81.8% for con- dition B. Of those patients who un- derwent phacoemulsification after trabeculectomy with MMC, the probability of treatment success at 5 years for patients who underwent phacoemulsification more than 1 year after trabeculectomy with MMC was 92.6%, whereas for patients who underwent phacoemulsification within 1 year of trabeculectomy with MMC, the corresponding prob- ability of success was 48.0%. Using the Cox proportional hazard model, the authors found that for condition A, higher IOP prior to trabeculec- tomy was a risk factor for surgical failure (p=0.01). For condition B, significant risk factors included higher IOP prior to trabeculectomy (p=0.0006), as well as phacoemulsifi- cation within 1 year after trabeculec- tomy (p=0.04). The relative risk for surgical failure as defined by condi- tion B for patients undergoing pha- coemulsification within 1 year of trabeculectomy was 2.87, while the relative risk of surgical failure in- creased by 1.09 for each mm Hg ad- ditional pre-trabeculectomy IOP. Considering the complexities and risks associated with trabeculec- tomy surgery, it is vital to identify and understand risk factors for surgi- cal failure. This study suggests that phacoemulsification within 1 year of trabeculectomy is a risk factor for surgical failure. The authors suggest that this may occur via scarring of the bleb by post-phacoemulsifica- tion inflammation. While it has been attempted to address this question in prior studies, the present investigation uses the Cox propor- tional hazard model (a time-to-event analysis estimating the relative risk of surgical failure based on multiple patient characteristics) to estimate the relative contribution of individ- ual risk factors to trabeculectomy failure. However, with a borderline p-value and lack of an adjustment for multiple comparisons, further studies are warranted to support the authors' conclusion. While the statistical analysis is unique for this specific question, the study design introduces several limi- tations. As noted by the authors, the retrospective design introduces sus- ceptibility to bias from patient selec- tion and other factors. Another limitation is sample size: 37 patients underwent phacoemulsification, and only 10 underwent phacoemulsifica- tion within 1 year post-trabeculec- tomy. The data show that these 10 patients had a much lower probabil- ity of good long-term IOP control. However, given the small sample size, an analysis of baseline charac- teristics of this group compared to the other patients could have been informative. In addition, the article would benefit from an analysis of whether these patients' IOP control might have fared better had they been randomized to wait longer for their cataract surgery. It may have also been informative to provide an analysis of average IOP change after cataract surgery in these patients since cataract surgery itself can affect IOP. No patient details are presented to address the question of whether patients who underwent pha- coemulsification soon after tra- beculectomy might have had a more complex post-op course (e.g., flat an- terior chamber) contributing to sur- gical failure, or whether patients having phacoemulsification earlier within 1 year fared worse than those having it 12 months post-trabeculec- tomy. Another limitation is the use of multiple similar endpoints. The dis- tinguishing factor between condi- tion A and condition B is the IOP limit of 21 versus 18. This 3 mm Hg difference does not seem clinically significant given that target pres- sures for patients undergoing tra- beculectomy are usually much lower depending on the degree of glau- coma severity. However, including both of these endpoints doubles the number of statistical comparisons and could decrease the strength of the study's conclusions due to multi- ple comparisons. Another important issue is the post-phacoemulsification treatment regimen, which in this study in- cluded fluorometholone and lev- ofloxacin for 1 month. It is typical practice in the United States to use more potent topical steroids follow- ing phacoemulsification, especially for eyes that might be susceptible to inflammation, e.g., those with thick irides or those who have recently

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