Editors Selection IGR 21-3

Surgical Treatment: Drainage Devices II

Tanuj Dada

Comment by Tanuj Dada on:

90295 A Prospective Analysis of iStent Inject Microstent Implantation: Surgical Outcomes, Endothelial Cell Density, and Device Position at 12 Months, Gillmann K; Mansouri K; Ambresin A et al., Journal of Glaucoma, 2020; 29: 639-647

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Gillman et al. have performed a commendable study evaluating the 12 month surgical outcomes after implantation of iStent inject (two devices) combined with phacoemulsification. Fifty-four eyes of 42 patients with early to moderate POAG or PXF glaucoma were compared with two sets of controls − Group A: 30 un-operated other eyes; Group B: 25 unrelated eyes undergoing phacoemulsification alone

IOP decreased from 16.5 ± 4.2 mmHg at baseline to 15.1 ± 3.7 mm Hg (−8.7%; P = 0.004), while medications decreased from 1.8 ± 1.0 to 0.5 ± 0.9 (−72.2%; P < 0.001). In control group B, the IOP decreased from 16.3 ± 2.5 mmHg at baseline to 13.8 ± 3.5 mm Hg (−15.2%; P = 0.024).

Very wide variations in device positioning could be observed with ASOCT although device position was unchanged during follow up . Regression analysis elicited significant predictors including SC dilatation effect [risk ratio (RR) = 0.230; P = 0.003], greatest SC diameter (RR = 0.991; P = 0.049), extrusion of the most anterior device (RR = 0.993; P = 0.012), and gonioscopically visible devices (RR = 0.406; P = 0.040). The mean ECD decrease was 14.6% at 12 months which was comparable to a similar decrease in the control group B (−14.4%).

The main limitation of the study was that control group B patients were retrospectively enrolled and did not undergo ASOCT imaging.1,2

The study casts a shadow on the IOP lowering capability of two iStent injects combined with phacoemulsification

Additionally diurnal IOP fluctuation and medication wash-out was not performed. The important messages from this manuscript are:

  1. The study casts a shadow on the IOP lowering capability of two iStent injects combined with phacoemulsification. In the present study only 8.7% IOP reduction was reported at 12 months and if you take away the effect of standalone phacoemulsification on IOP,3 the contribution of the iStent inject does not seem to be of any significant clinical benefit.
  2. Although the device implantation appears to be a simple and safe procedure with a short learning curve, the wide variations in its depth and implications on IOP outcomes suggest that a more robust surgeon training is required.
  3. ASOCT measurement of the SC dilatation/diameter and visibility of the stent on gonioscopy are prognostic indicators for functional iStents.
In conclusion, the paper clarifies that the combination of phacoemulsification plus iStent inject appears to be the least effective of the MIGS procedures and warrants an expert consensus and ethical discussion from the glaucoma community on its continued usage in glaucoma patients.


  1. Zhao Z, Zhu X, He W, Jiang C, Lu Y. Schlemm's Canal Expansion After Uncomplicated Phacoemulsification Surgery: An Optical Coherence Tomography Study. Invest Ophthalmol Vis Sci. 2016;57(15):6507-6512.
  2. Rubinstein Y, Fogel-Levin M, Singer R, et al. Microarchitecture of Schlemm's Canal Before and After Cataract Extraction Surgery. J Glaucoma. 2019;28(8):727-731.
  3. Chen PP, Lin SC, Junk AK, et al. The Effect of Phacoemulsification on Intraocular Pressure in Glaucoma Patients: A Report by the American Academy of Ophthalmology. Ophthalmology. 2015;122(7):1294-1307.

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