We read with interest the recent publication by Garcia-Feijoo and associates of 1-year findings after implantation of the CyPass supraciliary micro-stent (Transcend Medical, Menlo Park, California, USA). While the efficacy and safety results reported appear very promising, a closer look leaves a number of unanswered questions and areas of concern, which may be beneficial to explain to readers of the article.

First and foremost, the safety profile of this micro-stent should be clarified. The discussion’s concluding sentence states that the CyPass can be successfully implanted with fewer complications compared to conventional surgery. Improved safety should be expected in line with findings of other “MIGS” (minimally invasive glaucoma surgery) procedures. For instance, the iStent trabecular micro-bypass stent (Glaukos Corporation, Laguna, California, USA) was associated with an 18% adverse event rate in 12 months. Similarly, the Hydrus Schlemm’s canal micro-stent (Ivantis Inc, Irvine, California, USA) combined with phacoemulsification, reported an adverse event rate of 20% in the first year. The present study, however, appears to have an adverse event rate over 70% within the same timeframe (46 adverse events reported for 65 eyes, with only 30 accounted for in the results). Further clarification of the nature and potential etiology of all adverse events would be welcome, as would acknowledgement of this high complication rate.

The headline efficacy results stated in the abstract and illustrated in the figures are based on 55 out of 65 eyes that had 12 months of available data. We wonder if these results incorporated data from up to 8 patients who had secondary surgery, as the 10 excluded patients already include 4 who withdrew from the study and 3 who were lost to follow-up. If so, the 12-month results could be misleading and go against the intended methodology correctly stated earlier in the paper, where reoperated eyes were planned to be excluded. A more valid (and inferior) efficacy result based just on eyes that did not have secondary surgery is only briefly reported in the last sentence of the results.

Another area where further detail would be of interest is in postoperative intraocular pressure (IOP)-lowering medication use. While the proportion of patients using 0, 1, 2, 3, and 4 medications plus the mean number of medications is described at baseline, only the mean number of medications is reported postoperatively. It is important to understand the proportion of patients who are medication-free following surgery, especially for the 44.6% who achieved an IOP <15 mm Hg and 25.5% with IOP <13 mm Hg.

Finally, no primary efficacy endpoint was set preoperatively. It would be useful to report results consistent with consensus recommendations for defining and reporting success, such as the World Glaucoma Association guidelines. Commonly reported interventional outcomes such as proportion of patients achieving an unmedicated IOP reduction >20%, rather than the mean % IOP change, would provide meaningful results that are more comparable with studies of other interventions.

We commend the authors’ frank acknowledgement in the discussion of the limitations of the present study but seek clarification of the points we have raised, and we keenly await further data of this innovative MIGS device.