Latest ophthalmic viscosurgical devices offer promising results

The viscoadaptive properties of the newest generation OVDs can be exploited to provide complete endothelial protection.

ByMichela Cimberle

The newest generation of ophthalmic viscosurgical devices can help surgeons in making every step of cataract and refractive lens exchange procedures safe and easy.

“For the last 25 years, OVDs (ophthalmic viscosurgical devices) have been the most common but also the most underestimated tool for phacoemulsification and IOL implantation,” Manfred Tetz, MD, said.

The characteristics of the latest viscoelastic substances, such as Healon5 (2.3% sodium hyaluronate, Advanced Medical Optics), can be exploited to provide complete endothelial protection, prevent capsular breaks and ensure perfect IOL centration, according to Dr. Tetz.

“Once these goals are achieved, there’s only posterior capsular opacification to worry about,” Dr. Tetz said. “If you know the tricks, surgery will be a treat.”

The viscoadaptive properties of Healon5, which change from cohesive to dispersive according to the physical situations in the eye during surgery, can be exploited to “compartmentalize the eye,” creating a protective barrier in some areas and allowing complete freedom of movement in other areas at the same time.

Pupil dilatation, capsulorrhexis and hydrodissection

In eyes with small pupils, Healon5 can be used for viscodilatation. After filling about 70% of the anterior chamber with viscoelastic, additional small bowline injections are made around the pupillary margin.

“The pupil is dilated, and no additional drugs or iris retractors are needed,” Dr. Tetz said.

At the capsulorrhexis stage, precision and safety can be greatly enhanced by the appropriate use of OVDs.

“The trick is to achieve a pre-designed rhexis. Fill the chamber up to 70% with Healon5, then add a small quantity of the substance at the center of the lens. This will create a ditch in the center of the capsule, with a rim of higher elevation around it, indicated by a rim reflex. When you start pulling the capsule, all forces are immediately directed along this higher elevation, and the capsulorrhexis will automatically and always go along the pre-designed rim,” Dr. Tetz said.

The “trick’’ can be taken to the ultimate challenge: the mature lens. If the same procedure is followed, even in the presence of a completely liquefied, milky white cataract, the capsulorrhexis can be pre-designed and performed safely and easily. No liquefied lens matter will invade the anterior chamber and obscure the view, he said.

For hydrodissection, the trick is the creation of a fluid escape channel toward the incision. Hydrodissection is started at the opposite side, and the moment the wave of fluid comes up to the lens, the balanced salt solution will enter the escape channel and pull some of the Healon5 outward.

“This minimizes the risk of the anterior chamber overfilling,” he said.

Phaco in safe compartments

Most OVDs leave the eye during phacoemulsification. With Healon5, the surgeon has the opportunity to keep the viscoelastic inside the eye and exploit its properties for better protection and control, Dr. Tetz said.

“You can compartmentalize the anterior chamber in an upper area and in a lower area and only work in the lower area. The fluid will only enter in the compartment where the surgical maneuvers are performed. By using low irrigation, low ultrasound power and high vacuum settings you can work free and undisturbed underneath the protective cushion of visco, which remains there and doesn’t disperse,” Dr. Tetz said.

By using mostly suction and a calibrated balance of occlusion and short breaks, fast and constant aspiration of the nucleus fragments can be achieved with limited fluid movements and minimum ultrasound. The trick is to create little turbulence because turbulence breaks the cohesion of viscoelastic molecules, he said.

Healon5 is like “a ball of wool, tightly wrapped,” Dr. Tetz said. “If you pull the thread slowly, it won’t break and will drop in a long, soft chain. But if you pull the thread rapidly, the wool fibers will rupture. In the same way, the binding forces keep the molecules of Healon5 together, if you move slowly. But if you move rapidly, the molecules break. By using the changing physical properties of this substance, we can create rupture chains toward the center of the eye, where we are working and a stable cushion of Healon5 above.”

A standard chopping technique can be used, but another possibility is what Dr. Tetz called “viscophacorotation,” a phaco procedure in which “the lens comes to the tip, rather than the tip to the lens.”

The phaco tip is placed to the side of the lens and slowly turned on. In a slow vortex, the viscoelastic lumps together and drags the lens material into the phaco tip. With little ultrasound and suction, the lens is completely emulsified. No tip movement takes place during the entire procedure, he said.

IOL implantation and viscoelastic removal

Healon5 can be used with all commercially available lenses and injectors, Dr. Tetz said. By utilizing his two-compartment technique, the IOL can be implanted and guided to perfect centration under maximum protection of the endothelium and capsule, while the viscoelastic is gently and thoroughly removed from the eye.

“Insert the lens, but don’t center it immediately after insertion. The high viscosity of Healon5 will allow the lens to remain decentered long enough to let you go under the edge of the IOL with your irrigation and aspiration tip. At this point, aspirate all the viscoelastic from behind the lens. All the turbulence will be within the capsule, and you will still be protected by your cushion of visco in the anterior chamber. As you aspirate, the lens will move and automatically fall into place, well-centered under your perfect, pre-designed rhexis. The movements of the lens will be perfectly visible due to the high transparency of Healon5,” Dr. Tetz said.

The remaining visco is then aspirated from the anterior chamber, moving the I&A to the optic surface of the lens.

Complete removal of Healon5 is mandatory to prevent postoperative pressure spikes. If regular Healon can be left in small quantities, not exceeding 20%, according to several studies, Healon5, which is 2.3 times more concentrated, should never exceed 7%.

“If you remove it completely, the chances of getting pressure spikes are zero, unless there is unrecognized glaucoma in the eye,” Dr. Tetz said.

Other OVDs with similar properties can assist the surgeon in doing these maneuvers. Viscoat (chondroitin sulfate, sodium hyaluronate, Alcon) is a possible option but, according to Dr. Tetz, does not give the same visibility and is not equally cohesive. DisCoVisc (sodium chondroitin sulfate 4%, sodium hyaluronate 1.65%, Alcon) may be a good alternative, but “the closest to perfection” is, in his opinion, Healon5.

“Of course there are grounds for further improvement,” he said. “We could design a viscoelastic that becomes even more stable, almost solid, when we use it to compartmentalize the eye and at the same time disperses into even smaller molecules where we need to have freedom of movement. In the end, what we want to achieve is an increasingly higher degree of safety and control.”

For more information:

Manfred Tetz, MD,can be reached at Augentagesklinik Spreebogen, Alt Moabit 101 B, 10559 Berlin, Germany; +49-30-3980980; e-mail: gm@atk-spreebogen.de; Web site: www.augentagesklinik-spreebogen.de. He has no financial interest in any of the companies or products mentioned in this article.

Advanced Medical Optics, maker of Healon5, can be reached at 1700 E. St. Andrew Place, Santa Ana, CA 92705 U.S.A.; +1-714-247-8200; fax: +1-714-247-8672; Web site: www.amo-inc.com.

Michela Cimberle is an OSN Correspondent based in Treviso, Italy, who covers all aspects of ophthalmology. She focuses geographically on Europe.