Ex-Press P50 device filtering failure due to non-visible intraluminal blockages.

Purpose: To describe Ex-Press P50 failures due to an internal blockage.

Methods: A retrospective series of 248 eyes of 219 patients with Ex-Press P50 surgery was conducted. Of these cases, 18 (7.2%) required surgical revision due to filtration failure with no visible blockages in the gonioscopy and no filtering bleb in the slit lamp examination. In all of these cases, we found fibrosis on the edges of the scleral flap. After dissecting the scleral flap, filtration through the implant was restored spontaneously in 10 (4.0%) cases. In two cases fibrous tissue was observed on the tip of the implant and was necessary to remove it. In 6 (2.4%) cases, there was no filtration despite no visible obstruction and attempts to restore the flow were unsuccessful, requiring extraction of the implant and reconverting to trabeculectomy. Two of the removed devices were sanded until the lumen was visible to ascertain the nature of the obstruction.

Results: In our series, the most common cause of failure was episcleral fibrosis. In 2.4% of the cases, the blockage was intraluminal and aqueous flow could not be restored.

Conclusion: In the Ex-Press P50 implant an internal blockage, that is not visible through the proximal or distal orifices, may be the cause of failure. Unblocking by surgical maneuvers is not feasible due to the intraluminal design. These cases can be solved by extraction of the implant and conversion to trabeculectomy.