This article is more than 5 years old. Information may no longer be current.
Newer viscoelastics give surgeons more options
New techniques with Healon5 allow surgeons to use the material’s cohesive and pseudo-dispersive properties to best advantage.
Click Here to Manage Email Alerts
TORONTO – Recently developed viscoelastic products combine the qualities of pseudo- dispersive and cohesive viscoelastic behaviors, and surgeons may find that this takes some getting used to. A surgeon here has developed techniques that take advantage of the new materials’ characteristics to make cataract surgery safer.
“There’s a lot of interest in this now because surgeons using Healon5 (sodium hyaluronate 2.3%, Pharmacia) realize there are some maneuvers that are different from before,” said Steve A. Arshinoff, MD, of the Eye Associates in Toronto. “If you want to get broad use of Healon5, it’s a lot better if you use it with the ultimate soft shell technique.”
Dr. Arshinoff developed the ultimate soft shell technique (USST), in which Healon5 is used in combination with balanced salt solution, to facilitate capsulorrhexis and other maneuvers.
“The USST is a new ophthalmic viscosurgical device strategy, based upon some of the concepts of the soft shell technique. It is designed to overcome the drawbacks of viscoadaptives, in the same way that the soft shell technique overcame the drawbacks of dispersive and cohesive viscosurgical devices,” Dr. Arshinoff said. Dr. Arshinoff first described the soft shell technique (SST) in 1995.
Dr. Arshinoff worked with Pharmacia, the manufacturers of Healon and Healon GV (sodium hyaluronate), during the development of Healon5, which exhibits both pseudo-dispersive and cohesive viscoelastic behaviors.
Dr. Arshinoff noted that he prefers to use the term “ophthalmic viscosurgical device” (OVD) instead of “viscoelastic” for these types of products, because the latter term is “imprecise, if not incorrect.”
He said an OVD must have high viscosity when it is stationary in order to maintain surgical spaces in the eye. It also must lose viscosity when it is injected through a cannula. “It has to have a rapid drop in viscosity as you increase the shear rate, the force to which you expose the OVD,” he said.
Healon5 is highly viscous at low shear rates — so solid, in fact that instead of beginning to flow when subjected to sudden, high shear rates, the molecules fracture.
“The bonds between the molecule chains exceed the bonds along the chains, so as the chain is rearranging its shape it actually breaks,” he said.
Dr. Arshinoff said there are two commercially available types of fracturable OVD — also known as viscoadaptives. These are Healon5 and iVisc Phaco, which is also called MicroVisc Phaco and BD Multivisc in some markets. The Bohus product is currently not available or approved for use in the United States, although it is sold in Canada, the United Kingdom and other markets. It is manufactured by Bohus Biotech in Sweden.
Adjusting technique
Viscoadaptive materials require some modifications of surgical technique to be used most effectively, Dr. Arshinoff said. He identified three technique changes the surgeon must make in adopting a viscoadaptive OVD.
These changes are incorporated in his USST, which uses the properties of Healon5 and balanced salt solution (the lowest viscosity water-based surgical fluid, hence “ultimate”) to stabilize the anterior chamber and yet facilitate movement of surgical instruments.
Capsulorrhexis
A challenge when performing capsulorrhexis under Healon5 is the material’s high viscosity.
“You can induce excellent pressure in the anterior chamber and get a nice, rounded capsulorrhexis, but when you try to pull the capsule around to make the rhexis, you’re pulling in a highly viscous medium. Surgeons don’t like to work in the viscous medium because they find it offers a lot of resistance,” Dr. Arshinoff said.
To avoid this problem, he advises using balanced salt solution in addition to the Healon5 in this stage of the USST.
He instructs surgeons to fill the anterior chamber three-quarters full with Healon5, then inject balanced salt solution under the viscoadaptive layer. Normally the solution would leak through the incision, but Healon5 blocks the incision and prevents loss of fluid.
“Because you have the injection cannula on the lens surface, the viscoadaptive moves up and is pressurized against the cornea,” he said. “You’ve achieved pressurization as if you’d used only a viscoadaptive because the pressure you induce now depends on the viscoadaptive blocking the incision.”
Healon5 allows the surgeon to control the intraocular pressure without losing fluid or risking collapse of the chamber. The balanced salt solution allows the surgeon to easily maneuver in front of the lens with only very low resistance.
“Now you have the benefits of a low viscosity surgical environment and high viscosity pressurization of the eye,” Dr. Arshinoff said.
Hydrodissection
Surgeons may also encounter challenges with viscoadaptives during hydrodissection. When the surgeon attempts to inject fluid under the capsule, the viscoadaptive may not allow the fluid to flow out of the incsion. It can block the incision and cause pressure to build up.
“You can raise the pressure in the eye to 60, 70, 100 mm Hg or higher before you start getting the OVD out of the eye, so it’s very difficult to do hydrodissection,” Dr. Arshinoff said. “Some people have done mini-hydrodissection to get around this, but that’s not really adequate hydrodissection for modern chopping techniques.”
Dr. Arshinoff suggests inserting the balanced salt cannula and wiggling it back and forth to fracture the viscoadaptive around the incision. This creates a small channel through which the hydrodissecting balanced salt solution can flow out of the eye.
“You have fluid continuity between the area around the lens and the wound, and now you can do as much hydrodissection as you want to. The viscoadaptive is resting against the cornea, not touching the wound, and it doesn’t interfere,” he said.
|
|
|
|
| Ultimate soft shell technique, step 3 (pre-IOL implantation). The anterior chamber is filled with viscoadaptive injected across the capsulorrhexis. The peripheral part of the capsular bag is filled with balanced salt solution in a manner similar to hydrodissection. The IOL can then be inserted. |
Lens implantation
The third challenge with viscoadaptives, Dr. Arshinoff said, is creating space in the capsular bag for IOL implantation. His approach to this in the USST is to blockade the capsular opening with the viscoadaptive and fill the capsule with balanced salt solution.
“If you can use a viscoadaptive to blockade the incision, why can’t you use it to blockade the capsulorrhexis?” he said.
“You inject the viscoadaptive across the capsulorrhexis. As you see it begin to go into the capsule, that’s when you change from your viscoadaptive syringe to your balanced salt syringe.”
The surgeon can then fill the bag with balanced salt solution in the same fashion as injection for hydrodissection, and it will not flow out of the eye. The IOL injector can be placed through the capsulorrhexis and the lens injected into the bag. The IOL cartridge blocks the incision and maintains the pressure in the eye. Because there is only saline in the capsular bag, the IOL can unfold without resistance.
Dr. Arshinoff advises making these changes when using Healon5; otherwise, surgeons may have some difficulty performing these surgical tasks because Healon5 is different from other OVDs.
“By thinking of variations of these [maneuvers], you can attack all sorts of problems and make them easier and safer. One of the advantages about viscoadaptives having the properties of multiple OVDs, depending on the fluid aspiration rate setting, is that they can help you when you have different types of probelms,” Dr. Arshinoff said.
For Your Information:
- Steve A. Arshinoff, MD, can be reached at The Eye Associates, 2115 Finch Ave. W, Ste. 316, Toronto, ON M3N 2V6 Canada; (416) 745-6969; fax: (416) 745-6724; e-mail: saaeyes@idirect.com.
- Pharmacia can be reached at 100 Route 206 North, Peapack, NJ 07977; (908) 901-8592.