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Editors Selection IGR 17-4

Surgical Treatment: Combined Phaco-microstenting: 2-year outcomes

Comment by Syril Dorairaj & Tiago Prata on:

69962 Two-Year COMPASS Trial Results: Supraciliary Microstenting with Phacoemulsification in Patients with Open-Angle Glaucoma and Cataracts, Vold S; Ahmed II; Craven ER et al., Ophthalmology, 2016; 123: 2103-2112

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Many patients who undergo cataract surgery have co-morbid glaucoma. However, conventional combined glaucoma-cataract procedures (phacotrabeculectomy) are rarely performed in eyes with mild-to-moderate disease due to complications and unpredictable results. In this context, micro-invasive glaucoma surgery (MIGS) is emerging as an alternative procedure. In this large multicenter randomized control trial (RCT), Vold and colleagues have evaluated 2-year safety and efficacy of supraciliary microstenting (CyPass Micro-Stent; Transcend Medical, Inc., Menlo Park, CA) for treating mild-to-moderate primary open-angle glaucoma (POAG) in patients undergoing cataract surgery.

The difference between the two groups favored microstent implantation. However,this difference only was about 2 mmHg at 24 months

More than 500 POAG patients (mean diurnal unmedicated IOP between 21 and 33 mmHg) were randomized to phacoemulsification only group or supraciliary microstenting with phacoemulsification (1:3 ratio). The authors reported a sustained IOP reduction in both groups, with 60% of controls versus 77% of microstent subjects achieving ≥20% unmedicated IOP reduction versus baseline at 24 months. Mean IOP reduction was 7.4 mmHg for the microstent group versus 5.4 mmHg in controls, and 59% of control versus 85% of microstent subjects were medication free. No vision-threatening microstent-related complications were reported.

The study certainly provides bold results and has some strong characteristics, such as its large sample size, design (RCT) and longer follow-up when compared to previous studies. However, some important aspects should be considered while interpreting its results. As per inclusion criteria, all eyes had to have unmedicated diurnal IOP between 21 and 33 mmHg at baseline (and ≥ 3 mmHg over screening IOP). As a result, mean baseline IOP for both groups was approximately 25 mmHg, which exceeds the usual mean IOP values of untreated POAG patients. This type of bias may have led to two important issues basically due to regression to the mean.

First, looking only at the results from the control group, one can perceive the surprising results in IOP reduction. Phacoemulsification as a single procedure led to a mean IOP reduction of more than 20% (5.4 mmHg) from baseline. This goes against most studies, which usually report a very modest mean IOP reduction (1.5-2 mmHg) following uncomplicated phacoemulsification in POAG patients. In this context, it is important to emphasize that it has been reported that as much as 38% of controlled POAG eyes may lose IOP control during the first year after cataract surgery.

Second, using the same rationale, the above mentioned bias may also have led to an artificially high magnitude of IOP reduction following supraciliary microstenting with phacoemulsification. In addition, it should be underscored that although the authors reported a statistically significant treatment difference between the two groups favoring microstent implantation, this difference only was about 2 mmHg at 24 months, which puts its clinical relevance into discussion.

To summarize, we congratulate the authors for conducting such a large interventional multicenter RCT. CyPass Micro-Stent Implantation combined with cataract surgery resulted in minimal complications and sustained 2-year reduction in IOP and glaucoma medication use. MIGS will most likely occupy the empty space between medication/laser and trabeculectomy/tubes in cases with mild-to-moderate glaucoma, however we still have much to learn about the longterm efficacy, cost-effectiveness and quality of life indicators.

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