Editors Selection IGR 20-3

Surgical Treatment: Drainage Devices III

Nils Loewen
Yousef Al Yousef

Comment by Nils Loewen & Yousef Al Yousef on:

80996 A Prospective Analysis of iStent Inject Microstent Positioning: Schlemm Canal Dilatation and Intraocular Pressure Correlations, Gillmann K; Bravetti GE; Mermoud A et al., Journal of Glaucoma, 2019; 28: 613-621

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The iStent and iStent inject are trabecular meshwork (TM) bypass devices used in an add-on procedure with cataract surgery,1,2 and this use pattern continues to be the most common one. This elegant prospective study by Gillmann et al. examines the anatomic changes caused by the iStent inject by anterior segment optical coherence tomography (ASOCT) and attempts to correlate them to IOP and glaucoma medications. The authors enrolled 25 eyes from 19 patients with open-angle glaucoma or PEX glaucoma and compared them to 13 control eyes. The authors found that device protrusion and larger Schlemm's canal (SC) diameters were associated with lower postoperative IOP (rs = −0.54;P=0.005 and rs = −0.43;P=0.04, respectively), whereas the distance between the devices' heads and SC was inversely correlated with SC dilatation (rs = −0.41;P=0.04).

How difficult it is to place TM bypass stents in a consistent and effective manner, even in expert hands

Interestingly, the average major and minor diameter of the temporal SC of implanted eyes was larger than in controls. However, similar effects were described following standalone cataract surgery3 possibly from a trabeculoplasty-like effect from TM stretch or ultrasound exposure during phacoemulsification4 that is absent when TM is removed comprehensively. 5 The authors discuss shortcomings, including a relatively low patient number and the fact that two iStents inject are implanted, which limits a device-specific assessment.

This study highlights how difficult it is to place TM bypass stents in a consistent and effective manner, even in expert hands. The authors do not mention that fibrosis6 or biofilm deposition7 can likely not be seen due to the limited resolution of ASOCT that might be responsible for the waning effect observed in larger studies.8,9


  1. Samuelson TW, Katz LJ, Wells JM, et al. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118:459-467.
  2. Samuelson TW, Sarkisian SR Jr, Lubeck DM, et al. Prospective, Randomized, Controlled Pivotal Trial of iStent inject Trabecular Micro-Bypass in Primary Open- Angle Glaucoma and Cataract: Two-Year Results. Ophthalmology. https://doi. org/10.1016/j.ophtha.2019.03.006.
  3. Zhao Z, Zhu X, He W, et al. Schlemm's Canal Expansion After Uncomplicated Phacoemulsification Surgery: An Optical Coherence Tomography Study. Invest Opthalmol Vis Sci. 2016;7:6507.
  4. Wang N, Chintala SK, Fini ME, Schuman JS. Ultrasound activates the TM ELAM-1/ IL-1/NF-kappaB response: a potential mechanism for intraocular pressure reduction after phacoemulsification. Invest Ophthalmol Vis Sci. 2003;44:1977-1981.
  5. Parikh HA, Bussel II, Schuman JS, et al. Coarsened Exact Matching of Phaco- Trabectome to Trabectome in Phakic Patients: Lack of Additional Pressure Reduction from Phacoemulsification. PLoS One. 2016;11:e0149384.
  6. Capitena Young CE, Ammar DA, Seibold LK, et al. Histopathologic Examination of Trabecular Meshwork Changes After Trabecular Bypass Stent Implantation. J Glaucoma. 2018;27:606-609.
  7. Shah M, Campos-Moller X, Werner L, et al. Midterm failure of combined phacoemulsification with trabecular microbypass stenting: Clinicopathological analysis. J Cataract Refract Surg. 2018;44:654-657.
  8. Esfandiari H, Taubenslag K, Shah P, et al. Two-year data comparison of ab interno trabeculectomy and trabecular bypass stenting using exact matching. J Cataract Refract Surg. 2018;608-614.
  9. Al Yousef Y, Strzalkowska A, Hillenkamp J, et al. Comparison of a secondgeneration trabecular bypass (iStent inject) to ab interno trabeculectomy (Trabectome) by exact matching. medRxiv 2020 (in press).

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