One of the most feared complications after glaucoma surgeries is hypotony and its consequences. New bleb forming devices or Minimally Penetrating Glaucoma Surgeries (MPEGS) have been developed to reduce complications like hypotony by offering a better flow control.1-3 Nevertheless, even with these innovative bleb forming surgeries that require the use of MMC, early hypotony and its consequences are still an issue.
The authors investigated the incidence of postoperative hypotony in eyes that had undergone XEN Gel Stent implantation. They also correlated the hypotony with possible risk factors (axial length, myopia, arterial hypertension). They included 170 consecutive eyes and the hypotony was defined numerically as IOP ≤ 6 mmHg. They found hypotony in 57% of the eyes.
No significant difference was found in the analyzed risk factors except for the axial length, a known risk factor for hypotony in conventional filtering surgeries. Since axial length was associated with hypotony, the authors divided the range of axial length values into four quartiles. And the eyes with the longest axial length (4th quartile) had the highest frequency of postoperative hypotony (72%) compared with the eyes with the shortest AL (1st quartile, hypotony in 28% of eyes).
The investigators hypothesized that the reason for the higher hypotony rate in longer eyes might be explained by the thinner scleral wall with potential leakage of aqueous humor adjacent to the XEN Gel Stent. However, the hypotony rate is very similar (53%) in the second eye of patients with hypotony in the first eye and the authors do not mention any modifications in the technique to prevent hypotony. If scleral characteristics conditioned the hypotony rate and surgical technique was similar a higher incidence could be expected.
Another interesting finding was that in eyes with simultaneous cataract surgery, the risk for postoperative hypotony was about 0.5-fold. However, this finding is difficult to interpret and would be interesting to know the long-term success rate in both groups as the authors only mention that there are no statistical differences in the four-week IOP.
Surgeons should be aware of this risk factor for hypotony when counselling patients with long axial length about the risks of the surgery
Limitations of the study are the retrospective setting and the follow-up period of 12 months only. Also, the inclusion of both eyes in 34 patients is a possible bias. Another limitation was the fact that at a certain point, the surgery technique changed and viscoelastic (Z-HealinR) started to be instilled into the anterior chamber at the end of surgery to avoid early hypotony.
The authors concluded that surgeons should be aware of this risk factor for hypotony when counselling patients with long axial length about the risks of the surgery.