EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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November 2012 micro-bypass stents in cataract current phacoemulsification to the overall pressure-lowering effect of the combined surgery. It is important to bear in mind New York Eye and Ear Infirmary ophthalmology residents (left to right) Ambika Hoguet, M.D., Kevin Rosenberg, M.D., Timothy Sullivan, M.D., and Peter Chang, M.D. following surgery is provided. The authors imply in the discussion that "advanced glaucoma" may have been the cause, but no information is provided to validate the extent to which this is the case or to exclude other factors. There are some significant limitations to this study that must be considered in evaluating the strength of the authors' conclusions. No specific exclusion criteria are provided, and it is unclear if consec- utive patients meeting the inclusion criteria were offered enrollment or if selected patients were excluded from participation based on factors such as the density of the cataract, the degree of IOP elevation, or the severity of glaucoma damage. Selective enrollment of patients, even if unintentional, may have had an effect on the study results. Although the authors claim that 77% of eyes achieved their target IOP at 1 year post-op, they also indi- cate that, even before surgery, 43% of the patients already had achieved their target IOP with a combination of medications and/or laser trabecu- loplasty. Although the authors stratified the data according to the number of stents (two versus three) placed in each patient, we feel it would be helpful to also see the out- come data stratified by the severity of glaucoma. The lack of a standard- ized protocol for discontinuing or restarting medications following sur- gery may also have confounded the results. It is unclear if the mean number of post-op glaucoma med- ications would have been decreased in either or both treatment groups or if the difference in medication use at 1 year would have been affected if such a standardized protocol had been employed. It is possible, for example, that there was a greater tendency on the part of the investigators to discontinue medica- tions in eyes that had received three as opposed to two stents or to main- tain pre-op medications in patients with more advanced glaucoma. As the authors concede, the observational nature of this study and lack of random assignment to treatment groups make it difficult to ascertain how much of the pressure- lowering effect and reduction in medication burden for these patients was due to the incremental contri- bution of each stent. Although the authors state that patients requiring "greater IOP control" had three stents implanted instead of two, no specific criteria for determining the desired post-op target IOP or the desired degree of IOP reduction (as a percentage of the pre-op IOP or an absolute value) were provided. Ran- dom assignment of patients to the two-stent or three-stent treatment groups would allow more accurate assessment of any additional IOP lowering, greater or more prolonged stability of IOP reduction, and addi- tional reduction in the number of post-op glaucoma medications Source: Paul A. Sidoti, M.D. achieved by the use of an additional stent. Additionally, the inclusion of both eyes of six patients may have introduced further bias. Despite its limitations, this study provides valuable data on the effectiveness of phacoemulsification combined with iStent placement in patients with cataract and coexisting glaucoma. The authors have demon- strated that the implantation of two or three trabecular micro-bypass stents combined with cataract surgery is both safe and effective, resulting in clinically significant IOP and medication reduction and the potential to achieve target IOP levels appropriate for all degrees of glaucoma severity. Moreover, the relatively greater reduction in the number of post-op glaucoma med- ications in the cohort of patients receiving three stents as opposed to that receiving two stents indicates that the effect of multiple stents may be additive. The excellent risk profile of this procedure as well as its minimal invasiveness (performed through a small corneal incision without any disturbance to the con- junctiva) minimizes its potential im- pact on future surgical management options for glaucoma and may make iStent placement a reasonable op- tion to enhance IOP control or re- duce medication burden in patients with glaucoma who are undergoing cataract surgery. Further work is warranted to clarify the relative effect of stent placement and con- that glaucoma is a chronic disease that is dynamic in many respects. Longer follow-up of patients in a study such as this is warranted to assess continued stability of IOP control, ascertain whether a differ- ential IOP-lowering effect between the two- and three-stent groups develops over time, and determine whether the need for fewer post-op glaucoma medications in the three- stent group is maintained. Contin- ued monitoring of the study patients for the development of long-term complications is also essential. Further studies comparing the iStent to different glaucoma treatment options, assessing its safety and effectiveness over longer follow-up periods, and using better guidelines for determining number of stents implanted in each patient would be valuable in understanding the relative merits of trabecular micro- bypass stent surgery and its role in glaucoma management. It will also be important to assess impact of the iStent implant in halting disease progression based on structural assessment of the optic disc and functional parameters such as visual field testing. EW References 1. Craven ER, Katz LJ, Wells JM et al. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moder- ate open-angle glaucoma and cataract: two year follow-up. J Cataract Refract Surg 2012; 38: 1339-45. 2. Fea AM. Phacoemulsification vs. pha- coemulsification with micro-bypass stent im- plantation in primary open-angle glaucoma: randomized double-masked clinical trial. J Cataract Refract Surg 2010; 36: 407-412. 3. Samuelson TW, Katz LJ, Wells JM et al. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology 2011; 118:459-67. 4. Speigel D, Wetzel W, Neuhann T et al. Coexistent primary open-angle glaucoma and cataract: interim analysis of trabecular micro- bypass stent and concurrent cataract surgery. Eur J Ophthalmol 2009; 19:393-9. Contact information Sidoti: PSidoti@NYEE.EDU EW RESIDENTS 73