Scleral fenestration does not improve deep sclerectomy results

A surgical maneuver opening a suprachoroidal pathway for the aqueous did not prevent poor results caused by bleb failure.

Issue: September 1, 2002

ByMichela Cimberle

A 3-mm-by-2-mm scleral fenestration performed in the bed of the sclerectomy exposes the choroid.

PISA, Italy – An attempt to improve deep sclerectomy results failed — but in the process provided a lesson in how the procedure works. The unsuccessful attempt to add an internal drainage pathway showed the importance of subconjunctival filtration for aqueous humor drainage.

“We performed a large scleral fenestration under the scleral lake in eight patients with open-angle glaucoma. This was based on the assumption that increasing suprachoroidal outflow might improve intraocular pressure [IOP] reduction and overcome the problem of subconjunctival filtration failure, which is often the cause of unsuccessful surgery,” said Marco Nardi, MD, of Pisa University Eye Clinic.

Dr. Nardi and colleagues hypothesized that a more effective internal drainage might prevent bleb-related problems such as cystic blebs, leakage and infection, he said.

Surgical procedure

The eight patients, four men and four women, were white and were between 56 and 80 years old.

“After the two deep sclerectomy flaps were performed and the deeper one was dissected, we checked with a sponge that the aqueous was regularly flowing out. Then we performed a large (3-mm-by-2-mm) scleral fenestration in the bed of the sclerectomy, exposing the choroid (figure 1). A hyaluronic acid implant was inserted and the superficial scleral flap was sutured over the scleral lake with two 10-0 nylon stitches,” Dr. Nardi said.

Corticosteroid and antibiotic drops were administered from the first postoperative day.

IOP was measured at days 1 and 5, at 2 weeks and once a month during the following period. Ultrasound biomicroscopy (UBM) was performed at day 15 and at months 1 and 3 to evaluate the appearance of the deep sclerectomy site. Mean follow-up was 4 months.

Three patients (Nos. 1, 2 and 6) developed a cystic bleb 1 to 4 weeks after surgery with needling, subconjunctival fluorouracil injections and digital massage.

In seven patients, UBM showed a choroidal prolapse in the sceral lake. In only 1 patient did the suprachoroidal space increase in size during the follow-up.

Results

“The day after surgery we found some blood cells in the anterior chamber in two patients. No hypotony, no choroidal detachment and no cataract progression were reported,” Dr. Nardi said. The number of drugs needed dropped from an average of 2.75 per patient prop to 0.25 per patient postop.

The variation of tonometric values during the follow-up and the number of drugs administered to control IOP are reported in the table.

A significant complication

According to Dr. Nardi, three patients (Nos. 1, 2 and 6) developed a cystic bleb (figure 2) 1 to 4 weeks after surgery and were treated with needling, subconjunctival fluorouracil injections and digital massage. They showed a marked decrease in IOP immediately after the procedure, he said. One patient (No. 6) maintained target IOP without drugs throughout the follow-up.

The procedure failed in the other two patients, who afterward underwent a surgical bleb revision. One (No. 1) is now under control without additional therapy, while the second (No. 2) needs two drugs to maintain IOP under 18 mm Hg in the treated eye, Dr. Nardi said.

“In these patients the presence of an internal filtration and the blockage of external filtration were visible with UBM and confirmed by the marked decrease of IOP after needling. In this situation, a large suprachoroidal fenestration in the scleral lake bed should give the aqueous humor an alternative route of filtration from the scleral lake to the suprachoroidal space,” Dr. Nardi said.

“Unfortunately suprachoroidal fenestration did not result in good tonometric control in these cases. From a functional point of view, this shows that this route and the outflow through Schlemm’s canal — even if present — have a negligible importance on aqueous humor drainage after deep sclerectomy and confirms that subconjunctival drainage is crucial for the successful outcome of this surgery,” he said.

Scleral lake invaded

Ultrasound biomicroscopy gave further support to these conclusions.

“In seven patients, UBM showed a choroidal prolapse in the scleral lake (figure 3), and only in 1 patient did the suprachoroidal space increase in size during the follow-up (figure 4),” Dr. Nardi said.

“In quite a few cases the presence of the fenestration appeared to stimulate fibrosis in the scleral lake, increasing the normal rate of scleral lake obliteration. This may be due to a greater inflammatory response of the exposed choroidal tissue,” Dr. Nardi said.

The effects of scleral lake obliteration on IOP control are unknown at present, he said, and it is not possible to evaluate its importance in late deep sclerectomy failure.

The suprachoroidal space increased in size during the follow-up of one patient.

In quite a few cases the presense of fenetration appeared to stimulate fibrosis in the scleral lake.

For Your Information:

Marco Nardi, MD, can be reached at Ospedale Santa Chiara, Università di Pisa, Via Roma 67, 56100 Pisa, Italy; (39) 050 992599; fax: (39) 050 992976; e-mail: marco.nardi@med.unipi.it.