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72 EW RESIDENTS November 2012 EyeWorld journal club Review of “Using multiple trabecular patients to treat open-angle glaucoma” by Ambika Hoguet, M.D., Timothy Sullivan, M.D., Kevin Rosenberg, M.D., Peter Chang, M.D., and Paul A. Sidoti, M.D., program director, New York Eye and Ear Infirmary, New York Paul A. Sidoti, M.D. This month, I invited the New York Eye and Ear Infirmary residents to review this paper on micro-bypass stents, which is very timely in light of the recent FDA approval of the iStent. —David F. Chang, M.D., EyeWorld chief medical editor he iStent implant (Glaukos Corp., Laguna Hills, Calif.) is an ab interno trabecular bypass device that was recently FDA approved for use in patients with open-angle glaucoma who are undergoing cataract surgery. The iStent is among T a small but growing number of minimally invasive surgical treatments for glaucoma that are associated with significantly reduced rates of serious complications (such as infection, suprachoroidal hemorrhage, choroidal effusion, and ocular hypotony) relative to traditional external drainage procedures such as trabeculectomy and aqueous shunt implantation. There is growing literature supporting the relative effectiveness of the iStent in increasing the outflow facility of aqueous humor from the eye. Several authors have reported the effectiveness of single stent implantation in lowering IOP for patients with mild to moderate glaucoma.1-4 In “Using multiple trabecular micro-bypass stents in cataract patients to treat open-angle glaucoma,” published in the November Using multiple trabecular microbypass stents in cataract patients to treat open-angle glaucoma Graham W. Belovay, M.D., Abdulla Naqi, M.D., Brian J. Chan, B.H.Sc., Mahmoud Rateb, M.D., Iqbal (Ike) K. Ahmed, M.D. J Cataract Refract Surg (Nov) 2012; 38: 1911-1917 Purpose: To evaluate the efficacy of multiple trabecular micro-bypass stents combined with cataract surgery in patients with open-angle glaucoma (OAG) and cataract. Setting: Private practice, Mississauga, Ontario, Canada. Design: Comparative case series. Methods: Eyes with OAG had implantation of 2 or 3 micro-bypass stents with concurrent cataract surgery and follow-up through 1 year. Efficacy measures were intraocular pressure (IOP) and topical ocular hypotensive medication use. Safety assessment included complications and corrected distance visual acuity (CDVA). Results: The study comprised 53 eyes (47 patients); 28 had implantation of 2 stents and 25 had implantation of 3 stents. The overall mean 1-year post-operative IOP was 14.3 mm Hg, which was significantly lower than pre-operative IOP overall and in each group (P<.001). The target IOP was achieved in a significantly higher proportion of eyes at 1 year versus preoperatively (77% versus 43%; P<.001). Overall, 83% of eyes had a decrease in topical ocular hypotensive medication at 1 year from pre-operatively, with a 74% decrease in the mean number of medications (from 2.7 to 0.7) at 1 year (P<.001). The 3-stent group was on significantly fewer medications than the 2-stent group at 1 year (0.4 versus 1.0; P=.04). Conclusions: Using multiple micro-bypass stents with concurrent cataract surgery led to a mean post-operative IOP of less than 15 mm Hg and allowed patients to achieve target pressure control with significantly fewer medications through 1 year. Financial disclosure: Dr. Ahmed is a consultant to Glaukos Corp. No other author has a financial or proprietary interest in any material or method mentioned. issue of the Journal of Cataract & Refractive Surgery, Belovay, et. al. discuss the effects of using multiple trabecular micro-bypass stents at the time of cataract surgery to lower IOP and reduce medication burden in patients with coexisting glaucoma and cataract. The purpose of this study was to evaluate the safety and effectiveness of multiple stent implantations and to determine whether additional stents provided any incremental benefit with respect to IOP reduction and the need for glaucoma medications. As glaucoma remains a leading cause of blindness worldwide, we applaud the authors for attempting to further elucidate the clinical effectiveness of this new surgical alternative for lowering IOP and potentially limiting or preventing disease progression in patients with open-angle glaucoma. The current study was designed as an observational, open-label, nonrandomized, prospective, single-center study. A sample size of 53 eyes of 47 patients was included. As the term observational indicates, there was no control group or random assignment to treatment groups. Additionally, both the study patients and investigators were aware of the treatment (i.e., the number of stents) being administered. The inclusion criteria for this study were visually significant cataract “requiring surgery” and IOP that was poorly controlled on medications or that required >3 medications for adequate control. The severity of glaucoma for each patient (mild, moderate, or advanced) was determined using the clinical practice guidelines of the Canadian Ophthalmological Society. Each patient enrolled in the study underwent implantation of two or three iStents after phacoemulsification and IOL implantation. Post-op, the IOP and visual acuity were measured at 1 day, 1 week, and 1, 3, 6, and 12 months. There was no statistically significant difference in any of the pre-op characteristics evaluated for patients in the two-stent versus the threestent group. Overall, the results of the study pointed toward a favorable result in patients undergoing cataract extraction and multiple iStent placements. The authors reported a significant decrease in mean post-op IOP at 1 year, com- pared with the pre-op level for all patients (p<0.001), with 70% of eyes achieving an IOP of 15 mm Hg or less and 77% reaching their target IOP. This effect held up when evaluating the two- and three-stent groups separately. Although there was a slightly greater mean reduction in IOP following surgery for eyes in the three-stent (mean reduction 3.9 mm Hg) versus the twostent (mean reduction 3.5 mm Hg) group, this difference did not reach statistical significance (p=0.76). The mean number of glaucoma medications required to control IOP at 1 year post-op was reduced by 74% relative to the pre-op number for all patients (p<0.001). Adjunctive glaucoma medications were decreased from a pre-op average of 2.7 to an average of 0.7 one year following surgery with 83% of patients using fewer medications. Patients with three stents required significantly fewer medications at 1 year (85% mean reduction relative to pre-op number) compared with those receiving two stents (64% mean reduction relative to pre-op number) (p=0.04). During the 1-year follow-up period of the study, few complications were reported. The most common was blockage of the stent lumen, which was treated successfully using a YAG or argon laser in six of the eight eyes in which this occurred. From the authors’ description, it appears that the proximal opening of the stent in the anterior chamber became obstructed in these patients. It is unclear how frequently distal obstruction of a stent (not visible on examination or amenable to laser treatment) may have occurred. Other complications included one eye with hyphema and two eyes with a presumed steroid-induced IOP elevation. As the authors point out, this is a relatively safe procedure for most patients. The visual acuity outcome for patients in this study is somewhat concerning. The authors report that 15 (29%) of the patients had a corrected distance visual acuity (CDVA) at 1 year following surgery of 20/50 or worse. Five of these eyes demonstrated worsening CDVA relative to their pre-op level. Unfortunately, no explanation for either the reduction of CDVA or failure of CDVA to improve at 1 year November 2012 EW RESIDENTS 73 micro-bypass stents in cataract 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. Source: Paul A. Sidoti, 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 consecutive 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 indicate that, even before surgery, 43% of the patients already had achieved their target IOP with a combination of medications and/or laser trabeculoplasty. 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 outcome data stratified by the severity of glaucoma. The lack of a standardized protocol for discontinuing or restarting medications following surgery may also have confounded the results. It is unclear if the mean number of post-op glaucoma medications 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 medications in eyes that had received three as opposed to two stents or to maintain 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 pressurelowering effect and reduction in medication burden for these patients was due to the incremental contribution 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. Random 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 additional reduction in the number of post-op glaucoma medications 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 demonstrated 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 medications 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 conjunctiva) minimizes its potential impact on future surgical management options for glaucoma and may make iStent placement a reasonable option to enhance IOP control or reduce 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- current phacoemulsification to the overall pressure-lowering effect of the combined surgery. It is important to bear in mind 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 differential 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 threestent group is maintained. Continued 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 microbypass 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-moderate open-angle glaucoma and cataract: two year follow-up. J Cataract Refract Surg 2012; 38: 1339-45. 2. Fea AM. Phacoemulsification vs. phacoemulsification with micro-bypass stent implantation 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 microbypass stent and concurrent cataract surgery. Eur J Ophthalmol 2009; 19:393-9. Contact information Sidoti: [email protected]