ExPress Mini Shunt

Guest author

ANAM TARIQ

Ajmal Khan Tibbiya College

Aligarh, India

The ExPress Mini Glaucoma Shunt diverts aqueous from the anterior chamber to a subconjunctival reservoir without removal of scleral or iris tissue.

Background:

The ExPress Mini Glaucoma shunt was originally developed by Optonol Ltd for implantation under the conjunctiva for controlling intra-ocular pressure (IOP).

This biocompatible device is almost 3 mm long with an external diameter of approximately 400 microns. It is non-valved, MRI compatible, stainless steel device with a 50 microns lumen. 

It has an external disc at one end and a spur like extension on the other to prevent extrusion.

The unguarded technique of implantation under the conjunctiva caused various complications, such as:

• Hypotony
• Erosion
• Extrusion of implant
• Endophthalmitis

To avoid these complications, implantation under the scleral flap is being performed.

Surgical technique:

Topical or retrobulbar anesthesia is administered depending on patient selection and surgeon preference.

Step 1: A standard fornix or limbal based conjunctival incision is performed to gain exposure to scleral bed adjacent to the limbus. Gentle cautery is performed in this area.

Step 2: A scleral flap is created in a manner similar to what is performed in a standard trabeculectomy.

Care is taken to direct the flap upto clear cornea.

Anti-fibrotic agents can be applied either before or after the creation of the scleral flap in the usual manner based on the surgeon's preference.

Step 3: A temporal paracentesis is created through the cornea.

The scleral flap is lifted and care is taken to identify the centre of the "blue line" adjacent to the clear cornea which corresponds to the location of the trabecular meshwork.

A 26-gauge needle is inserted into the anterior chamber through the centre of the "blue line" at an angle parallel to the Iris plane. Any lateral movement of the needle, especially when removing, should be avoided as this will cause aqueous to flow around the implant.

Step 4: The ExPress Mini shunt is preloaded on an injector. Fitted into the lumen of the shunt is a metal rod that is attached to the end of the injector.

The shunt is then placed in the anterior chamber through the ostium created with the needle. The angle of the entry with the shunt is the same as the angle used to make the ostium. The shunt is inserted all the way into the wound the plate flush with the scleral bed.

In some procedures standard punctal plug inserter, the injector has an area on the shaft that is depressed which retracts the metal rod in the lumen of the shunt.

Step 5: The scleral flap is then sutured in place using 10-0 nylon suture on a spatulated needle. One to three sutures are typically required depending on the flow which can be tested by inflating the anterior chamber with balanced salt solution using a 27 or 30 gauge cannula through the temporal paracentesis.

Step 6: The conjunctiva is then meticulously closed with the surgeon's suture of choice.

Relative contraindications:

Congenital and juvenile glaucoma, aniridia and anterior segment dysgenesis, phakic primary angle closure glaucoma, pseudophakic glaucoma with an anterior chamber intra-ocular lens, neovascular glaucoma, patients with thin sclera.

Absolute contraindications:

• Acute attack of angle-closure glaucoma.
• Microphthalmia.
• Nanophtalmos.

Complications:

1. Early postoperative high IOP: Due to overfilling of anterior chamber with viscoelastic. Only 1/3rd of anterior chamber should be filled with viscoelastic.

2. Early postoperative hypotony, loss of anterior chamber depth and choroidal detachment: Overfiltration can be avoided by a large securely sutured scleral flap. In case of implant-iris touch the AC can be filled with viscoelastic or a pressure bandage/ double padding/ Simmon's shell can be used.

3. Implant-iris touch: A misplaced incision which is not parallel to the Iris can lead to implant-iris touch. In cases of significant Iris indentation by the ExPress shunt, especially phakic patients, the device should be repositioned. The shunt is explanted, a new track made and the implant re-inserted. In order to facilitate removal of the ExPress Mini shunt it should be rotated so that the spur becomes horizontal, the wound enlarged by a 15' blade and the implanted removed.

4. Extrusion of implant: This can occur spontaneously or following trauma.

5. Malposition of ExPress shunt and it's consequences: A malpositioned implant can erode the conjunctiva. That is also an indication for repositioning of the shunt.

6. Long term corneal endothelial cell loss: Anterior implantation of the shunt can cause endothelial cell damage especially in the superior cornea.

7. Infection: Use of Antimetabolites increases the risk of infection. However, it is not clear whether the device should be removed if endophthalmitis ensues.

8. MRI safety: The patients can undergo MRI scans 2 weeks after implantation and withstand upto 3 Tesla. However, it is not known what will be effects if more than 3 Tesla are required/used.

9. Economic consideration: The cost of the device (Rs 33,000 in India. Approximately 465 USD) is too high for most self-paying patients and this premium cost may itself put unrealistically high expectations regarding the success of the procedure in the patients.