UBM reveals mechanism of action of deep sclerectomy with hyaluronic acid implant

A filtering bleb, low-reflective scleral tissue around the lake and a supraciliary hypoechoic area were correlated with postop IOP reduction.

ByMichela Cimberle

VERONA, Italy — A filtering bleb is present in a high percentage of eyes treated with deep sclerectomy and reticulated hyaluronic acid implant, according to an investigation carried out with ultrasound biomicroscopy. The study also revealed other aspects of the filtration induced by this type of surgery.

The study was conducted on 30 patients with primary open-angle glaucoma, treated with deep sclerectomy and SK-Gel implant (Cornéal) by Giorgio Marchini, MD, of Verona University Eye Clinic. UBM was performed 1, 3, 6 and 12 months after surgery and then every 6 months, using the UBM P40 System (Paradigm Medical Industries).

“By ultrasound biomicroscopy we evaluated the morphology and changes of the decompression chamber during the follow-up, the presence of a filtering bleb and the reflectivity of the scleral tissue around the decompression space. Also the presence of a supraciliary hypoechoic area was investigated. These findings were then correlated with clinical findings and postoperative results on intraocular pressure,” Prof. Marchini said.

Figure 1. The UBM appearance of deep sclerectomy with reticulated hyaluronic acid implant 1 month postop. The trabeculo-Descemet’s membrane (arrow) and the decompression space (asterisk) are clearly visible. The presence of RHAI cannot be assessed because it is not echoic. (Printed with permission from the Journal of Cataract and Refractive Surgery, Vol. 27, April 2001, p. 511.)

Figure 2. Same case as in figure 1. The UBM image shows a scan parallel to the limbus, close to the angle of the anterior chamber. The arrow indicates the trabeculo-Descemet’s membrane and the asterisk indicates the decompression space. (Printed with permission from the Journal of Cataract and Refractive Surgery, Vol. 27, April 2001, p. 511.)

Decompression chamber

UBM showed that a decompression chamber was present and remained unchanged for up to 3 months. Scar tissue had partly reduced the space in 8 patients at 6 months and had completely invaded the space in 2 patients at 1 year. Other patients maintained a well-opened lake throughout the follow-up.

“The reduction in size of the decompression chamber was associated with reduced IOP-lowering efficiency. However, we found that surgery may fail even in the presence of a decompression chamber. Two patients in whom surgery failed had in fact a well-opened decompression chamber but no sign of aqueous outflow. It is likely that scarring tissue attacked the walls all around the lake and prevented filtration,” Prof. Marchini said.

UBM was unable to determine the time of absorption of the SK-Gel implant, as this was invisible by UBM. Prof. Marchini said the tight fit of the triangular implant into the lake leaves no space for ultrasound responses. Also, the molecule of hyaluronic acid is permeable by ultrasound and therefore produces no reflected echoes.

Three signs of filtration

Three factors connected with IOP lowering were detected by UBM in various combinations.

A conjunctival bleb of various sizes was detected by UBM in 18 of the 30 patients (60%) and was also visible on slit lamp examination.

“Reflectivity of the bleb also was evaluated, as low reflective blebs have proven to be associated with a greater IOP lowering effect and better filtration. Low reflective blebs were more numerous in our series, as they were found in 15 of our 18 patients,” Prof. Marchini said.

In 14 patients (47%), low reflective tissue was also found around the decompression chamber and was also interpreted as a sign of filtration.

“There were cases where hyporeflective tissue created a sort of connection between decompression chamber and conjunctival bleb. In at least three patients the low reflectivity of this portion of the sclera was the only detectable sign of filtration, and was actually associated with reduced IOP,” he said.

Finally, a supraciliary hypoechoic area was detected in 18 cases.

“In these patients, IOP was lower than in other patients. Also, in one case where the hypoechoic area was the only UBM sign present, adequate IOP levels were achieved,” he said.

“What we saw was sufficient to determine a possible mechanism of action of deep sclerectomy. The presence of a bleb in so many cases suggests that external filtration plays a role that is more important than expected. Other ways of filtration, as suggested by our observations, may be the uveoscleral and transscleral,” he said.

Figure 3. A deep sclerectomy with reticulated hyaluronic acid implant 12 months postop. The IOP is 13 mm HG, and the decompression space (ds) is clearly visible. Note the simultaneous presence of the three UBM characteristics associated with aqueous outflow: a filtering bleb (asterisks), a thin supraciliary hypoechoic area (small arrows) and an area of scleral hyporeflectivity lateral to the decompression space (large arrow). (Printed with permission from the Journal of Cataract and Refractive Surgery, Vol. 27, April 2001, p. 513.)

Figure 4. Same case as in Figure 3. The image shows a scan parallel to the limbus passing through the pars plicata of the ciliary body. The ciliary processes are visible inferiorly. Note the decompression space (ds) and the three UBM characteristics found to be associated with aqueous outflow: a filtering bleb (asterisks), a thin supraciliary hypoechoic area (small arrows) and an area of scleral hyporeflectivity lateral to the decompression space (large arrow). (Printed with permission from the Journal of Cataract and Refractive Surgery, Vol. 27, April 2001, p. 513.)

For Your Information:

Giorgio Marchini, MD, can be reached at Clinica Oculistica, Università di Verona, Ospedale Borgo Trento, P.le Stefani 1, 37126 Verona, Italy; +(39) 045-807-2340; fax: +(39) 045-807-2025; e-mail: oculist@borgotrento.univr.it. Dr. Marchini has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Cornéal can be reached at 31 Rue des Colonnes, 75012 Paris, France; +(33) 1-43-42-9393; fax: +(33) 1-43-07-0190; e-mail: export@corneal.com.

Paradigm Medical Industries can be reached at 2355 South 1070 West, Salt Lake City, UT 84119 U.S.A.; +(1) 801-977-8970; fax: +(1) 801-977-9128; Web site: www.paradigm-medical.com.