May 2007

 

CATARACT/ IOL

 

Holding it together

 


by Maxine Lipner EyeWorld Senior Contributing Editor
   

Ensuring that cataract incisions stay sealed may be as simple as gluing them together

The structural properties of fibrin adhesive are similar to a human plasma clot.

Source: John Hovanesian, M.D.

Fibrin adhesive is an extremely flexible material.

Source: John Hovanesian, M.D.

Cataract surgeons aim for tight incisions to keep harmful bacteria at bay. While most of them use incisional construction or suturing to accomplish this, John A. Hovanesian, M.D., clinical instructor, Jules Stein Eye Institute, UCLA, Los Angeles, has been investigating a unique approach: using fibrin adhesive to seal closed cataract incisions.

Dr. Hovanesian, Laguna Hills, Calif., recently launched a pilot study on this topic using eight eye bank corneas. The study, in which a fibrin adhesive known as Tisseel (Baxter Healthcare, Deerfield, Ill.) was used, was spurred by concerns about the risk of endophthalmitis. “Every surgeon who is using a clear corneal incision—unless they suture it, and most do not—is concerned that his incision closure may not be adequate, that there may be an increased risk of endophthalmitis,” he said. “We’re looking for a better but non-sutured way to close wounds.”

Comparing cataract wounds In the study, investigators compared how well four typical cataract wounds using no adhesive fared compared to four eyes in which fibrin was used to seal the incision. An artificial anterior chamber was used to mimic normal pressure in those eyes and then the wounds were tested to see how completely sealed they were. “We tested for outflow of fluid by pressing on the wounds using instruments,” Dr. Hovanesian said. “In addition, we replicated the method that Peter McDonnell [M.D., director, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore] used in a study that he did on eye bank eyes using India ink.”

In the study of clear corneal incisions, which appeared in the December 2003 issue of Ophthalmology, India ink was applied to cadaver eyes to detect the possible flow of fluid along the incision. Then, by raising and lowering the infusion bottle, investigators were able to vary IOP and mimic what would occur when patients successively blinked their eyes.

When Dr. Hovanesian tried the two different approaches with the eyes with and without the Tisseel glue, he found that there was a clear distinction between the groups. “In the four eyes that had no adhesive, India ink easily was drawn into the wound when pressure was reduced to near zero, which happens potentially after cataract surgery,” he said. “Meanwhile, in the four eyes where we used the adhesive, there was no India ink that was drawn into the wound— it clearly prevented both ingress and egress of fluid.”

Proper application technique

Tisseel glue comes in two separate vials and requires preparation time in the operating room. “It takes about 20 minutes for the nurses to warm it,” Dr. Hovanesian said. “Then once it is prepared, the glue can be used for four hours.”

Surgeons should also note that that it’s important not to use too much of the material “because it will form a [messy] coagulum, and it gets in the way of a smooth surface at the end of surgery,” Dr. Hovanesian said. “The other thing is that fibrin adhesive provides the strongest bond when it’s a thin layer between two structures being sealed together, so you want to use just a little of it.”

For the cataract wounds, the idea was to apply the fibrin while minimally watering down the glue with aqueous from the anterior chamber, keeping the two parts of the adhesive separate until they were inside the cataract wound. To accomplish this, Dr. Hovanesian said he lowered the pressure in the eye to “near zero,” which is similar to what practitioners would encounter after putting in a lens implant and removing the viscoelastic but before inflating the eye to pressurize it. Using the same kind of metal slit knife that he routinely relies on to create a cataract incision, Dr. Hovanesian painted the top surface of the blade with fibrinogen and the bottom surface with thrombin. “I used less than a drop of each,” he said. “Then, without cutting the wound further, the blade was inserted into the wound and then removed.” The two parts were then brought into contact to respectively coat the front and the back surfaces of the wound, and when the blade was withdrawn, the two mixed so that they would stick together.

While Tisseel has been used for several ophthalmologic purposes, including pterygium surgery, LASIK, and even the prevention of epithelial ingrowth, one of the limitations to its use in cataract surgery is concerns about safety. “The limitation in cataract surgery is that we’re not yet fully aware of its intraocular safety profile,” Dr. Hovanesian said.

The general safety of the product, however, has been quite good. “Tisseel has been in use around the world for more than 26 years and has been used in more than 11 million surgeries,” he said. “Although it is a product made from human and cow blood, there have been no cases of HIV, hepatitis, or BSE (bovine spongiform encephalopathy).”

Practitioners have only just begun to tap into Tisseel’s potential for use with ophthalmologic surgery. “It’s a subject that deserves a lot of discussion and really deserves many of the great minds in ophthalmology to think about different ways to use these products because it does not need to be limited to ocular surface surgery,” Dr, Hovanesian said. “I think that there is also great potential in glaucoma surgery and retinal surgery, and we’ve only begun to scratch the surface of those applications.”

Editors’ note: Dr. Hovanesian is a consultant for Baxter BioScience (Beltsville, Md.), IOP, Inc. (Costa Mesa, Calif.), and DuPont (Wilmington, Del.).

Contact Information

Hovanesian: 949-742-3937, johnhova@cox.net

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