spotlight on technology & technique
Going with the Flow
For the first time, limbal filtration using an implant appears to be a safe and effective means of treating glaucoma.
By Christopher Kent, Senior Associate Editor

Now an innovative device that's been used in Europe to safely alleviate pressure in the anterior chamber is available in the United States through CIBA Vision. The Ex-PRESS Mini Glaucoma Shunt (developed by Optonol Ltd., a high-tech engineering company based in Israel and Switzerland) is a 400-micron diameter stainless steel tube, less than 3 mm long. When surgically implanted at the limbus, it reduces IOP by diverting excess aqueous humor from the anterior chamber to a subconjunctival bleb.

Unlike other glaucoma drainage devices, the Ex-PRESS shunt is designed to be a simpler substitute for trabeculectomy. Clinical studies have shown that the shunt effectively lowers IOP to safer levels and reduces dependence on glaucoma medications.

The shunt features:

• a blunt, beveled tip designed to insert easily with minimal damage to ocular tissue
• an external flange to prevent over-penetration
• a spur to prevent extrusion and keep the shunt where you place it
• three transverse orifices to allow uninterrupted aqueous humor flow if the main orifice opening is blocked by the iris
• a no-valve flow modulating mechanism in the main lumen, to control aqueous outflow
• a specially designed disposable inserter, mounted on a disposable syringe.

Implanting the Shunt

The procedure can be performed using topical or retrobulbar anesthesia. To implant the shunt, the surgeon makes a small incision in the conjunctiva about 8 mm from the limbus in the supranasal or supratemporal quadrant and dissects a path to the limbus in the plane between the sclera and Tenon's capsule.

The Ex-PRESS Mini Glaucoma Shunt, available from CIBA Vision.

After filling the anterior chamber with viscoelastic, the surgeon uses a 26-gauge needle to create a track into the anterior chamber at the limbus. The inserter is then used to place the Ex-PRESS shunt into the tunnel made by the needle. Once the inserter is withdrawn, the conjunctival wound is sutured closed and the anterior chamber is refilled with viscoelastic.

The high viscosity of the viscoelastic limits the initial outflow through the shunt and maintains a safe IOP during the period of time it takes for the bleb to form. Nevertheless, during the initial day or two following surgery, IOP usually drops to between 5 and 10 mm Hg, and it remains at that level for 7 to 10 days. This has been associated with a low rate of complications.

Eventually, the formation of a bleb creates homeostasis and IOP is maintained between 10 and 20 mm Hg. (The eye clears the viscoelastic from the anterior chamber within a few days.)

Surgeons who have performed the procedure report that post-op care is similar to care following a trabeculectomy: steroids every 2 hours for about 1 week, followed by tapering, and topical antibiotics for 1 week.

Advantages of the Procedure

According to CIBA Vision, the implantation procedure for the Ex-PRESS shunt has several advantages over conventional filtering surgery:

• The procedure is minimally invasive; the tiny size of the shunt only requires a very small incision in the conjunctiva. Also, implantation requires minimal tissue manipulation and no scleral dissection or cauterization, reducing the extent of trauma, inflammation and scarring. No iridectomy is needed, which may reduce the likelihood of cataract formation.
• Implantation can be completed in a fraction of the time of conventional filtering surgery.
• Use of topical anesthesia is recommended.
• The procedure is reversible.
• The procedure is reproducible; surgical results and IOP reduction are highly predictable from case to case.

The procedure also appears to be quite effective. A multicenter study evaluating the safety and efficacy of the Ex-PRESS R-50 Mini Glau-coma Shunt found that after 2 years:

• 83.3% of eyes had an IOP less than 21 mm Hg (a 35% drop in IOP, on average) without intra-operative usage of antimetabolites.
• The overall average number of glaucoma medications used by participants dropped by more than two-thirds.

Feedback from the Field

James E. Memmen, M.D., chairman of the Department of Ophthalmology at Prevea Clinic, Inc., in Green Bay, Wis., has used the Ex-PRESS shunt since the summer of 2002. "It's much easier to do this procedure than trabeculectomy, and it produces similar positive results. So far, I see no reason to think that patients won't continue to do beautifully. However, it hasn't produced fewer complications than trabeculectomy."

	Once the bleb has formed, IOP usually stabilizes between 10 and 20 mm Hg. Results appear to be maintained at 2 years.

Dr. Memmen says he's learned a lot from his experience so far. "For one thing, the Ex-PRESS shunt leaves patient pressures lower than nonpenetrating surgery. This is an important factor when deciding which procedure is right for a given patient. Also, it's crucial to make the pathway using a needle as close as possible to the size of the shunt. A 25-gauge needle was too large; some patients' pressures dropped to 2 or 3 mm Hg.

"Creating a means to do limbal filtration surgery using an implant has been attempted many times; this is the first one that's worked. Is it perfect? No, but it clearly has the potential to cause a paradigm shift in the way we treat glaucoma, especially if complication rates fall lower than trabeculectomy."

Karanjit Singh Kooner, M.D., associate professor of ophthalmology at the University of Texas South-western Medical Center in Dallas, has used the Ex-PRESS shunt since November. "So far, I've done eight eyes in seven patients," he says. "At 8 weeks of follow-up, the pressure drop has averaged 40%, and 80% of the patients are no longer using glaucoma meds.

"The Ex-PRESS shunt has more in common with trabeculectomy than with other implant shunts. It also has several advantages over trabeculectomy. You manipulate tissue less during the surgery, so post-op follow-up is much quieter. Because the entry wound is the same every time, and the instrument has a flow restriction device, the drop in IOP is more predictable. Post-op inflammation is minimal, so you don't have to use steroids very often. And patients' eyes aren't red, as they often are after trabeculectomy."

Both doctors agree that the learning curve is more challenging than it appears at first. "The size of the implant is so small that you need to be very precise," notes Dr. Kooner. Nevertheless, both doctors are upbeat about the future of the device.

"I believe this could be used as the initial surgical procedure when treating glaucoma," Dr. Kooner concludes. "We're very comfortable using it that way."

The Future Looks Bright

The Ex-PRESS shunt has received the CE Mark and FDA marketing clearance; it should be available in Canada this year. However, before performing the procedure, surgeons must complete a training course offered by CIBA Vision.

Contraindications for use of the Ex-PRESS glaucoma shunt include angle-closure glaucoma, pre-existing pathology that could cause postoperative complications, or disease such as uveitis, ocular infection, severe dry eye or severe blepharitis.

For more information about the Ex-PRESS shunt, contact CIBA Vision at (800) 845-6585, or visit
www.cibavision.com/products/surgical solutions/Ex-PRESS.shtml on the Web.