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Editors Selection IGR 20-4
Surgical Treatment: Outcomes of a Schlemm Microstent Implantation
Comment by Nils Loewen on:
78011 A Schlemm Canal Microstent for Intraocular Pressure Reduction in Primary Open-Angle Glaucoma and Cataract: The HORIZON Study, Samuelson TW; Chang DF; Marquis R et al., Ophthalmology, 2018; 0:
In this randomized controlled study, Samuelson et al. followed 556 patients for 24 months and compared IOP and medication after Hydrus implantation (Ivantis, Inc, Irvine, CA) combined with cataract surgery versus cataract surgery alone. The Hydrus is made out of nitinol, nickel-titanium alloy, and has a length of 8 mm1 spanning about 76°. Like the iStent (Glaukos, San Clemente, CA) made of titanium, it is implanted through viscoelastic under direct gonioscopic visualization. The study had an adequate sample size and was rigorously designed.
The differences between both groups were surprisingly small: Hydrus patients had a 2.2 mmHg larger IOP reduction than control patients (Hydrus: −7.6 ± 4.1 mmHg (mean ± standard deviation, SD), control: −5.3 ± 3.9 mmHg control). 19.5% more Hydrus than control patients had a more than 20% IOP reduction (Hydrus: 77.3%, control: 57.8%). Similarly, the Hydrus reduced medications by 0.4 more than the control (Hydrus: 1.7 ± 0.9 to 0.3 ± 0.8, control 1.7 ± 0.9 to 0.7 ± 0.9). The results are strikingly similar to the seminal iStent study,2 in which 18% more iStent eyes achieved an IOP reduction of more than 20% compared to controls.
The results are strikingly similar to the seminal iStent study, in which 18% more iStent eyes achieved an IOP reduction of more than 20% compared to controlsIn this Hydrus study, patients had an IOP of about 18 mmHg prior to and 25 mmHg after washout. One can compute this as an IOP reduction to 18 mmHg (Hydrus) and to 20 mmHg (controls).
Cataract surgery can cause an IOP drop on its own.3 Interestingly, such a trabeculoplasty- like effect is not present in MIGS procedures that ablate the TM, like the Trabectome (Neomedix Inc., Tustin, CA).4,5
Because Schlemm's canal has septations that hinder circumferential flow, a single opening (e.g., iStent) provides access to approximately 60° of outflow channels.6 The Hydrus would be predicted to achieve access to nearly 120° when disrupting Schlemm's canal septations 60° apart. It is interesting that the Hydrus does not appear to be fundamentally better than the iStent despite this advantage. Recent reports found a biofilm buildup7 and fibrosis8 that occlude the lumen of the iStent. This might explain the declining efficacy compared to TM ablation as observed in a study using Exact Matching9 and also affect the Hydrus.
References
- Shareef S, Fea A, Ahmed IIK. The Hydrus Micro-stent. In: Samples JR, Ahmed IIK (eds.), Surgical Innovations in Glaucoma, pp. 171-174. Springer, New York, 2014.
- Samuelson TW, et al. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118:459-467.
- Mansberger SL, et al. Reduction in intraocular pressure after cataract extraction: the Ocular Hypertension Treatment Study. Ophthalmology. 2012;119:1826-1831.
- Neiweem AE, Bussel II, Schuman JS, Brown EN, Loewen NA. Glaucoma Surgery Calculator: Limited Additive Effect of Phacoemulsification on Intraocular Pressure in Ab Interno Trabeculectomy. PLoS One. 2016;11, e0153585.
- Parikh HA, Bussel II, Schuman JS, Brown EN, Loewen, N. A. Coarsened Exact Matching of Phaco-Trabectome to Trabectome in Phakic Patients: Lack of Additional Pressure Reduction from Phacoemulsification. PLoS One. 2016;11, e0149384.
- Rosenquist R, Epstein D, Melamed S, Johnson M, Grant, WM. Outflow resistance of enucleated human eyes at two different perfusion pressures and different extents of trabeculotomy. Curr Eye Res. 1989;8:1233-1240.
- Shah M, Campos-Möller X, Werner L, Mamalis N, Ahmed IIK. Midterm failure of combined phacoemulsification with trabecular microbypass stenting: Clinicopathological analysis. J Cataract Refract Surg. 2018;44:654-657.
- Capitena Young CE, et al. Histopathologic Examination of Trabecular Meshwork Changes After Trabecular Bypass Stent Implantation. J Glaucoma. 2018;27:606-609.
- Esfandiari H, et al. Two-year data comparison of ab interno trabeculectomy and trabecular bypass stenting using Exact Matching. J Cataract Refract Surg. 2018; doi:10.20944/preprints201811.0109.v1
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