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Editors Selection IGR 17-3
Surgical Treatment: Ab Interno Trabeculotomy
Comment by Ronald Fellman on:
66510 Transient Ciliochoroidal Detachment After Ab Interno Trabeculotomy for Open-Angle Glaucoma: A Prospective Anterior-Segment Optical Coherence Tomography Study, Akagi T; Nakano E; Nakanishi H et al., JAMA ophthalmology, 2016; 134: 304-311
Hypotony induced ciliochoroidal detachment (CCD) is well described after filtration or tube shunt surgery, but is not yet associated with canal-based surgery. Canal surgery only eliminates 50% of the trabecular outflow resistance, so it seems unusual that hypotony would develop, unless there was another mechanism. However, the authors of this study found an inexplicable high rate of CCD (42%), in the immediate postoperative period, after canal-based Trabectome (NeoMedix Corp) surgery. The authors found evidence with anterior segment OCT of direct communication between the AC and the suprachoroidal space, indicating an unintended cyclodialysis cleft. However, they did not mention a shallow chamber nor any gonioscopic documentation that would directly corroborate their findings. This is a very high rate of CCD for an angle procedure. Pilocarpine is well-known to aid in keeping a cyclodialysis cleft open and this drug was used post operatively in all cases. The preoperative use of Pilocarpine was not mentioned.
Although many factors contribute to the amount of flow and IOP postoperatively, scleral flap construction and placement and tension on sutures are important things to consider
Johnstone and Smit reported many years ago that viscodilation of SC with viscocanalostomy created multiple small 'trabeculotomies'. In an analogous manner, it is very feasible that Trabectome may create multiple small nearby cyclodialyses as detected with the high resolution OCT. Simple gonioscopy would have likely revealed a cyclodialysis cleft, but this was not done. In addition, it is possible the back wall of the canal may be abraded during Trabectome, removing the endothelial barrier allowing the seepage of aqueous into the deep sclera and into the suprachoroidal space. This may be another mechanism, but is purely speculative.
However, we still have to consider other mechanisms of effusion possibly related to the shape of the eye, as CCD was more common in shorter eyes. Is it possible the arc of the trabecular meshwork and canal is more acute in smaller eyes making it more likely to detach the CB or abrade the back wall in certain areas? The most common cause of a CCD after glaucoma surgery is low IOP, but in this case, an unintended cyclodialysis cleft may be the initiating factor that led to low IOP. Surgeons need to start documenting the degree of difficulty of the Trabectome procedure with special reference to the ease of device passage with IOP and potential creation of an unintended cyclodialysis cleft. Careful postoperative gonioscopy will clarify this important imaging observation.
Thus, there are multiple plausible factors that can explain transient CCD including, the creation of an unintended cyclodialysis cleft, choroidal effusion associated with a short eye triggered by transient hypotony, acute lowering of IOP, and seepage of aqueous into the suprachoroidal space from nearby damaged deep sclera. Further studies with combined gonioscopy may better clarify the authors' exciting observation.
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