UBM demonstrates better anatomic results of laser-assisted deep sclerectomy

A more predictable, regular profile of the internal structures enhances brisk, long-term outflow.

NAPLES, Italy – The use of an excimer laser improves the anatomic and functional results of deep sclerectomy, enhancing precision, reliability and predictability of the procedure, according to a study carried out by a group of ophthalmologists in Rome. The study was presented by Vittorio Picardo, MD, and Marina Modesti, MD, at the meeting here of the Italian Ophthalmologic Society.

“We have noticed a better technical quality when the laser was used in performing the deeper scleral flap,” said Dr. Picardo. “There was far less tissue damage, the internal surfaces of the decompression chamber came out more even and regular and the pre-Descemetic membrane was never too thin or too thick. As a result, filtration was better.”

The study compared the results of two groups of five eyes each, treated for primary open angle glaucoma (POAG) with either manual (group 1) or laser surgery (group 2), using ultrasound biomicroscopy (UBM) to monitor the anatomic changes during follow-up. Patients had similar mean age and preoperative IOP levels (mean 25 mm Hg). In the second group the excimer laser was used to open the second scleral window, while the first flap was performed with a knife.

“We used the Technolas C 217 laser from Bausch & Lomb, performing a triangular ablation with the aid of a Cantera-Olivieri masking device (Meditekno, Rome). In both groups we used either the Corneal (Paris, France) hyaluronic acid SKGel or the STAAR (Monrovia, Calif.) collagen AquaFlow drainage implants,” said Dr. Picardo. Three other colleagues participated in the study: Scipione Eossi, MD, Paolo Michieletto, MD, and Alessandra Balestrazzi, MD.

Significant differences

“We evaluated all filtering structures and their variations at 1, 3 and 4 months of the follow-up,” said Dr. Modesti, presenting UBM images of the two groups.

“Postoperatively, conjunctival blebs looked spongy, large and quiet, and, except in one case in group 1, maintained a constant thickness throughout the follow-up. Also the decompression chamber, in all 9 successful cases, showed no variations. In one patient of group 1, there were adhesions between the iris and the pre-Descemetic membrane, resulting in reduced aqueous filtration. In all cases in group 2, the scleral lake maintained a constant depth and diameter.”

The pre-Descemetic membrane was measured at month 4, to avoid misleading results due to remnants of the drainage implants at the bottom of the lake.

At first glance, mean values seem to be comparable in the two groups but, as Dr. Modesti pointed out, the minimum and maximum values are very different. The laser-treated pre-Descemetic membranes have very similar, near average thicknesses, while manual surgery produced a greater variability of results.

How deep to go

“With the laser, we can calculate exactly how deep we want to go,” said Dr. Modesti. “We evaluate microscopically the scleral thickness, set the machine and let it perform the task. At any rate, the excimer laser stops ablating as soon as the aqueous percolates through the membrane. Manual surgery can never be so precise. We can have a zero-thickness, which means that the membrane has been perforated, or a membrane that is too thick and allows poor filtration.”

The pre-Descemetic membrane profile also appeared more regular when the laser had been used. Dr. Modesti specified that the membrane was always measured at its thinnest point.

Microperforations produced by manual surgery were also documented by UBM images.

Radial sections gave evidence of lateral intrascleral filtration. The aqueous appeared to penetrate into the scleral tissue like a sponge.

In the same way, filtration over the ciliary body and the choroid was visualized in curvilinear space, following the profile of the ciliary body and the choroid, which remained with only small variations during the follow-up of both groups.

“This physiological space is there also before surgery,” Dr. Modesti pointed out. “However, whenever we have performed a preoperative UBM, we have noticed that it becomes larger after surgery.”

“In all our cases, we could establish a correlation between functional and anatomic results. In 9 out of 10 patients postoperative IOP was less than 20 mm Hg without additional therapy. In one case of the manually operated group, Latanoprost therapy was necessary to lower IOP levels. This patient developed a cystic, non-filtering bleb, and a lake that at 3 months had reduced depth and diameter,” Dr. Picardo said.

“From these results, we can say that deep sclerectomy is effective with both techniques,” he said in concluding the presentation. “However, UBM gave us the great opportunity of seeing our results in more detail, and details can make a lot of difference.”

Cantera-Olivieri masking device in place on the eye.	The masking device helps produce a triangular ablation.
Postoperatively, conjunctival blebs looked spongy, large and quiet.	Postoperatively, conjunctival blebs looked spongy, large and quiet.
The decompression chamber, in all successful cases, showed little variation.	The decompression chamber, in all successful cases, showed little variation.
Laser treated pre-Descemetic membranes had near-average thicknesses...	... while manual surgery produced more variability of results.
The pre-Descemetic membrane appeared more regular when the laser was used.	Microperforations of pre-Descemetic membrane produced by manual surgery are seen.
Radial sections give evidence of lateral infrascleral filtration.	The aqueous appears to penetrate the tissue like a sponge.
Filtration through the ciliary body and choroid could be seen in a curvilinear space, following the contour of the tissue.	Filtration was maintained throughout follow-up with only minimal variations.
The physiological space is present before surgery...	... but seems to increase in size postoperatively.
The bleb and scleral lake before surgery...	...and after successful surgery.
One patient in the manually operated group developed a cystic, non-filtering bleb...	...and a lake that at 3 months had reduced depth and diameter.

For Your Information:

• Vittorio Picardo, MD, and Marina Modesti, MD, can be reached at Studio Oculistico, Via Nomentana 311, 00162 Roma, Italy; (39) 06-8547845; e-mail: eyeboss@vpicardo.it. Dr. Picardo and Dr. Modesti have no direct financial interest in the products mentioned in this article, nor are they paid consultants for any companies mentioned.