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Sclerothalamotomy ab interno a minimally invasive surgical option for glaucoma
Stable IOP was observed over a period of 2 years, with few postoperative complications.
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PARIS – Sclerothalamotomy ab interno is a surgical option for glaucoma that is as effective as trabeculectomy in lowering IOP but with fewer potential complications, according to Bojan Pajic, MD, a glaucoma specialist at the Klinik Pallas in Olten, Switzerland.
“In all ab externo surgical techniques, penetrating and nonpenetrating, there is a possibility that fibroblasts from the conjunctiva migrate into the scleral tissue and proliferate there, blocking filtration. Sclerothalamotomy (STT), which is penetrating surgery with an ab interno, transcameral approach, prevents this risk and restores effective internal filtration through the internal episcleral and uveoscleral channels,” he said at last year’s meeting of the French Society of Ophthalmology.
Similar to other surgical methods, STT ab interno circumvents the trabecular meshwork resistance by creating a drainage canal in the sclera, but the site of perforation is reached from the inside, and four sclerectomy sites are created using a special high-frequency diathermy probe. These sites are called “thalami,” from the Latin for “inner chamber,” he said.
Diathermy probe
“The probe, which is produced by Oertli Instruments, has a 1-mm long platinum tip with a diameter of 0.3 mm, bent at an angle of 15°. The outer diameter of the probe measures 0.9 mm. The high-frequency diathermic probe is equipped with an inner platinum electrode, which is isolated from one of the returning coaxial electrodes. A source of bipolar energy raises the temperature of the tip to 130°C, while the rest of the instrument stays cool,” Dr. Pajic explained.
The instrument is inserted into the anterior chamber through a 1.2-mm nasal incision in clear cornea and directed to the opposite side, toward the angle. The operating field is visualized using a four-mirror goniolens. Using the tip of the probe, four 0.3 mm deep and 0.6 mm wide sclerotomy sites are created, for a total absorption surface of 2.4 mm². Tobradex and pilocarpine drops are instilled postoperatively and over the next 10 days.
“STT ab interno creates a direct access for the aqueous humor between the anterior chamber and Schlemm’s canal. A constant outflow is restored and a permanent reduction of intraocular pressure is achieved,” Dr. Pajic said.
Long-term IOP reduction
In a prospective study, the results of STT ab interno in 61 patients operated between April and August 2002 were analyzed. There were 53 cases of open-angle glaucoma, four cases of pseudoexfoliative glaucoma, three cases of neovascular glaucoma and one case of juvenile glaucoma. Mean patient age was 69 years (range 10 to 82 years). In all cases, medical therapy was insufficient to control IOP.
“Results [with STT ab interno] were very encouraging. In the 53 patients with open-angle glaucoma, the mean preoperative IOP was 25.7 mm Hg, ranging between 18 and 48 mm Hg. One month after surgery, it lowered to 16.9 mm Hg, ranging between 9 and 44 mm Hg. Between 6 and 21 months, the mean IOP values were constantly between 14 and 16 mm Hg, and no patient had IOP over 20 mm Hg. These data are fairly long term and statistically significant,” Dr. Pajic said.
A similar trend was observed in the other groups, although the numbers were not sufficient to be statistically evaluated.
In the patient with juvenile glaucoma, IOP was reduced from 38 mm Hg preop to 12 mm Hg postop, and results were stable 24 months after the treatment.
“More recently, we have operated on more patients with juvenile glaucoma, which are not included in the study. All of them have obtained an optimal control of the IOP,” Dr. Pajic noted.
The use of preoperative medications in all groups dropped from a mean of 2.6 drops before surgery to a mean of 0.26 drops after surgery.
Fewer complications
Complications were few and transient, Dr. Pajic said. Unlike trabeculectomy and deep sclerectomy, STT ab interno is rarely the cause of postoperative hypotony, he said. Only one case was observed in Dr. Pajic’s series, probably due to a transient interruption of aqueous humor secretion, which lasted 3 days. Hyphema occurred in six cases (three of them were neovascular glaucoma) and resolved spontaneously within 2 weeks. A transient fibrin formation in the pupil region was observed in one eye and treated with steroid drops.
A temporary increase in IOP after surgery was reported in 10 eyes, which were treated with pressure-reducing eye drops. In the majority of the cases, the treatment was gradually discontinued and IOP was lowered to the target range within 2 months.
“IOP elevation can be quite normal in the first week after surgery as a consequence of tissue reparation. However, this is only a transient event and long-term obstruction of the aqueous pathway has never been observed,” Dr. Pajic said.
Since the ab interno approach prevents fibroblast migration from the conjunctiva, fibrosis does not occur. Moreover, histology has shown that the diathermy probe does not cause coagulation or cellular necrosis and that the lining of the aqueous channel remains intact, Dr. Pajic said.
“Therefore, the scleral channel performed by STT ab interno remains open and functional, and this ensures an efficacy and longevity of filtration, which is probably superior to that of trabeculectomy and deep sclerectomy,” he noted.
Another advantage of STT ab interno is the shorter surgical time.
“While trabeculectomy takes at least half an hour, STT ab interno can be carried out in about 5 minutes, and it is much easier to learn and to perform,” Dr. Pajic said.
If STT ab interno fails, he said, patients can still be treated with other surgical options, as the minimally invasive approach of STT ab interno leaves space for other procedures.
For Your Information:
- Bojan Pajic, MD, can be reached at Klinik Pallas Augenzentrum, Louis Giroud Strasse 20, CH-4600 Olten, Switzerland; +41-62-2866200; fax: +41-62-2866220; e-mail: bpajic@datacomm.ch. Dr. Pajic has no financial interest in the diathermy probe.
- Oertli Instruments can be reached at CH-9442 Berneck, Switzerland; +41-71-747-4200; fax: +41-71-747-4290; e-mail: info@oertli-instruments.com; Web site: www.oertli-instruments.com.
- Michela Cimberle is an OSN Correspondent based in Asolo, Italy.