Fig. 10.1
The Hydrus Microstent. The material used in the production of this microstent is nitinol, an extremely elastic and biocompatible metal used for cardiovascular and orthopaedic implants. Nitinol also has memory form properties and consequently is an ideal support structure in the Schlemm Canal. Once it has been positioned, the microstent allows the formation of scaffolding for the Schlemm Canal that permits access to the multiple collector canals that drain the aqueous humor from the trabeculate. The Hydrus Microstent has a proximal opening that allows the trabeculate to remain patent, minimizing the possibility of obstructions: in this way, a communication pathway is guaranteed between the AC and the SC, without damage to the trabeculate. The microstent has an ‘open frame’ configuration with windows that allow an obstruction-free outflow of the aqueous humor to the collector canals. The most promising version is 8 mm long, with an almost circular shape; it dilates the SC up to 166 μm for the entire length and for 241 μm at the opening
Fig. 10.2
Dedicated device for the insertion of the Hydrus Microstent . A dedicated device is used for the insertion the microstent in the SC
Surgical Technique
As for the other MIGS techniques, even though this procedure is easier than other glaucoma surgeries, we would recommend local anesthesia (retrobulbar or peribulbar) when the learning surgeon is performing his first implant procedures. Preoperative instillation of miotic eyedrops (1–2% pilocarpine) is recommended to open the angle. For this type of surgery, the surgeon assumes the sitting position described in Chap. 7 for goniotomy, in Chap. 8 for the iStent and in Chap. 9 for the trabectome: he will position himself on the side opposite to the portion of the angle he intends operating on; the patient’s head is slightly rotated to the opposite side from the surgeon. The operating microscope is tilted 30–45 degrees to permit optimal visualization of the angle.
The first surgical steps are the same as those described in Chaps. 7–9. They are as follows:
Step 1: creation of a 1.5 mm incision in clear cornea, in a temporal position and parallel to the iris;
Step 2: introduction of VES in the AC;
Step 3: placement of gel on the cornea, on the goniolens and control of the vision of the angle; Normally a modified Swan-Jacobs lens: high magnification is recommended (10–12×). Having identified surgical landmarks (the trabeculate localized between the scleral spur and the Schwalbe line), the surgeon enters the AC with the device.
Fig. 10.3
The device approaches the camerular angle (step 4)
Fig. 10.4
(a, b) The microstent is positioned in the Schlemm Canal (step 5). The microstent is positioned in the Schlemm Canal by exerting soft pressure on the dedicated plunger of the device (a and b)
Fig. 10.5
Withdrawal of the insertion device from the AC (step 6). The insertion device is gently removed.– Step 7: visualization and control of the correct position of the insert. Following insertion, the microstent must lie parallel to the trabeculate.– Step 8: the viscoelastic is removed.– Step 9: hydrosuture and possible additional sutures of the corneal incision. After the hydrosuture, the surgeon must check that there is no leakage; if leakage is observed, a suture in 10.0 nylon is positioned
Fig. 10.6
(a, b) Outflow of the aqueous humor following implantation of the Hydrus Microstent . As mentioned previously, the microstent increases and maintains the conventional outflow of the aqueous humor through the creation of an opening in the trabeculate and by dilating a significant portion of the SC that exploits the circumferential outflow to the multiple collector canals (a and b). Given that the Hydrus Microstent can be positioned through a small incision in clear cornea (1.5 mm), it can be associated with micro-incisional surgery of the cataract (MICS)
Results
According to several clinical studies, this device is efficacious in eyes affected by primary mild-moderate open-angle glaucoma and pseudo-exfoliative glaucoma. As mentioned previously, the pressure-lowering effects are greater when associated with cataract surgery. The efficacy and the initial safety profile have been confirmed by clinical studies; it has been reported that complications are observed in just 1% of cases and are mainly transitory post-operative inflammation.
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