Stent suture improves flow control with Baerveldt implant

Advantages include more reliable early pressure control without sudden decompression later.

Issue: January 15, 2006

ByBob Kronemyer

A simple stenting technique using a ripcord-type suture improves the predictability of aqueous outflow and postoperative IOP without the need for an external ligature when using the Advanced Medical Optics Baerveldt glaucoma implant, according to one clinician.

“The Baerveldt glaucoma implant offers a high level of success in long-term IOP control for recalcitrant glaucoma because there is a larger surface area for aqueous absorption,” said Keith Barton, MD, FRCP, FRCS, FRCOphth, consultant ophthalmologist and glaucoma service director at Moorfields Eye Hospital in London. “But the reason the Baerveldt is not as widely used as some other glaucoma implants is that it lacks a mechanism of flow control, which can cause very severe hypotony in the early postoperative period.”

Early hypotony has traditionally been prevented by ligation of the tube portion of the implant, he said.

Insertion of the Supramid stent suture. The distal end is left under the conjunctiva.

The Supramid suture extends into the anterior chamber.Images: Barton K

“The ligature prevents any aqueous flow through the tube in the early postoperative period, and then absorbs about 5 weeks after surgery with a reduction in IOP,” Dr. Barton explained. “However, the difficulty with this technique is that the IOP may remain high for the first few weeks after surgery and then drop precipitously when the ligature dissolves after approximately 5 weeks. This precipitous drop in IOP may result in severe sequelae, such as choroidal hemorrhage, in a significant minority of patients.”

This sudden loss of pressure can be circumvented partially by the use of an additional stent suture. “However, most stent sutures that have been described do not provide sufficient resistance by themselves to reliably prevent early complications,” Dr. Barton said. “An external ligature is still required.”

Tight entry site

In 1993, Sherwood and colleagues described a technique using a 3-0 nylon braided Supramid suture as a useful adjunct to external ligation, Dr. Barton said. Dr. Barton and colleagues have developed this idea into “a simple and safe technique whereby this stent suture can be used without external ligation when combined with a tight scleral entry site.”

The technique produces physiological IOP levels in the early postoperative period, he said, and is advantageous because normal pressure is achieved from day 1 with no sudden drop in IOP later.

Acute Chemical burn [photo]
Constriction of the tube around the Supramid stent suture at the anterior chamber entry site (25 gauge) provides additional resistance, thereby preventing hypotony.

Acute Chemical burn [photo]
This technique allows some titration of aqueous flow on the operating table.

The stent suture is threaded up the middle of the tube implant, and provides about 90% occlusion. “However, stenting alone does not reliably prevent postoperative hypotony,” Dr. Barton said. “With our technique, the Supramid suture is introduced through a tight scleral entry site into the anterior chamber using a 25-gauge rather than the traditional 23-gauge needle stab. This squeezes the tube slightly around the stent suture. Having that slight extra resistance at the anterior chamber entry site is the key to preventing hypotony. This results in much more reliable early flow control.”

The smaller entry site is beveled at its external opening to facilitate the entry of the tube, he said.

Study results

At the annual meeting of the Association for Research in Vision and Ophthalmology, Dr. Barton and his colleagues shared the results of a prospective study of 62 consecutive first eyes implanted with the Baerveldt implant using the new technique. The average patient age was 48.6 years, and average follow-up time was 11.3 months.

On day 1, IOP decreased from the preop mean of 26.6 mm Hg on 2.4 topical glaucoma medications to 20 mm Hg. IOP dropped as low as 12 mm Hg on 1.3 medications after 2 years. At the last follow-up, 77% of eyes were controlled within the normal range without medication, and 19% were controlled with topical medication. No eyes were uncontrolled, Dr. Barton said.

“In our study, only 30% of stent sutures had been removed at 1 year,” Dr. Barton said. The stent suture is eventually removed in most eyes.

Complications included one iris blockage, one tube-corneal touch, two exposures, three ligations for hypotony, two vitrectomies for misdirection and one retinal detachment. There were no suprachoroidal hemorrhages.

“Our study compares favorably in terms of safety and efficacy with previous studies using external ligation,” Dr. Barton said. “However, the trick is having a tight entry site. The regular 23-gauge entry site is too large for this technique. Additionally, it is becoming popular to insert tubes through a long scleral tunnel. While this helps prevent extrusion, tube insertion through the tunnel is more fiddly, and some surgeons compensate by making the entry site a little larger than normal, eg, 22 gauge. This increases the risk of postoperative hypotony and is incompatible with our technique.”

As to why Dr. Barton and his associates continue to use the Baerveldt implant at all, “there is still a strong argument for using this implant in more recalcitrant glaucoma patients,” Dr. Barton said. “It is flexible and has a very low profile on the eye surface. Consequently, the implant disturbs surrounding tissues less on eye movement and excites less of a foreign body tissue reaction. This may explain why the Baerveldt seems to have a lower tendency to encapsulate than other implants. The larger surface area also provides a greater area for aqueous absorption, thereby optimizing IOP control.”

For Your Information:
Keith Barton, MD, FRCP, FRCS, FRCOphth, can be reached at Moorfields Eye Hospital, 162 City Road, London, EC1V 2PD, United Kingdom; 44-207-566-2256; fax: 44-207-566-2608; e-mail: keith1barton@aol.com.
Bob Kronemyer is an OSN Correspondent based in Elkhart, Ind.