August 2007

 

CATARACT/ IOL

 

Protective qualities of dispersive viscoelastic material


by Rich Daly EyeWorld Contributing Editor

   

Study quantifies the long-assumed endothelial cell protection provided by OVD during cataract surgery

Preservation of endothelial cells during cataract surgery and placement of posterior chamber IOLs has long been a critical goal for surgeons.

Dutch researchers compared the abilities of cohesive and dispersive ophthalmic viscoelastic devices (OVDs) to protect the corneal endothelium following in-the-bag phacoemuslification with implantation of a foldable posterior chamber IOL. Their study, published in a recent issue of Acta Ophthalmologica Scandinavica, clearly showed that using a dispersive hyaluronate OVD during phacoemulsification may allow for protection of the endothelial cells while suppressing the formation of free radicals.

The prospective single-masked randomized study divided 60 eyes of 60 cataract patients into three groups of 20 patients, on whom a different OVD was used: Celoftal (hydroxypropyl methylcellulose, Alcon, Fort Worth, Texas), Vitrax (sodium hyaluronate 3%, AMO, Advanced Medical Optics, Santa Ana, Calif.) or Healon (sodium hyaluronate 1%, AMO). The investigators evaluated the corneal response to surgery through pre-op and three-month post-op measurements of endothelial cell loss, variation in mean cell area of endothelial cells, frequency of hexagonal cells, and central corneal thickness. Post-op, all three groups had a significant decrease in cell count, but the decrease was significantly less in the Vitrax group (6.97%) than in the Celoftal (18.03%) and Healon groups (18.46%). No changes in cell area variation, hexagonality, or corneal thickness were observed within any of the three groups or among the groups.

The investigators credited the superior effect of Vitrax to its ability to reduce formation of free hydroxyl radicals, which have been reportedly destructive to corneal endothelial cells. Previous research has found hyaluronate OVDs can suppress the formation of free radicals and exert anti-inflammatory effects. Studies also have demonstrated that dispersive hyaluronate OVDs suppress free radicals better than cohesive hyaluronate OVDs.

D. Michael Colvard, M.D., assistant clinical professor, Keck School of Medicine, University of Southern California, Los Angeles, said that this is the first study to detail specifically the endothelial protective effect of Vitrax, a dispersive sodium hyaluronate product. “Ophthalmologists have believed for some time that low molecular weight sodium hyaluronate OVDs tend to have excellent coating properties and are more protective of the corneal endothelium than either methylcellulose OVDs or high molecular weight sodium hyaluronate products. This small study has limitations, but it seems to support this belief. Dr. Colvard said.

Satish S. Modi, M.D., assistant clinical professor of ophthalmology, Albert Einstein College of Medicine, New York, said larger endothelial cell loss found by the researchers with Celoftal and Healon makes sense because it does not take much flow rate to remove them.

“Since Celoftal (which is not available in the United States) is used only to coat the inside of the IOL cartridge, and not for cataract surgery, it would have been better if the investigators had used a more commonly used dispersive OVD, such as Viscoat (chondroitin sulfate 4%/ sodium hyaluronate 3%, Alcon). The study results are more applicable in third world cataract procedures, where Celoftal is still heavily used”, Dr. Modi said. His procedures rely more on Viscoat, another dispersive OVD, which research has found to provide significantly better endothelial protection than a cohesive OVD, or indeed, all other dispersive OVDs. Dr. Modi said research in which he has participated concluded that Viscoat, and a more viscous dispersive, DisCoVisc (sodium chondroitin sulfate/sodium hyaluronate, Alcon), provide the best available protection. Though Viscoat can be difficult to remove and can result in large post-op IOP spikes, there are no such problems with DisCoVisc.

Study faults highlighted

Surgeons praised the study’s prospective randomized design with a single surgeon using a standardized technique and equipment, along with the use of objective, rather than subjective, criteria of surgical endothelial trauma.

However, surgeons said the research would have had more impact if the investigators specified the various densities of nuclei involved, the amount of phaco power used, or the length of phaco of time in each patient.

“I would wonder whether a few particularly dense or difficult cases could skew the average cell loss values given the relatively small sample size of each group,” said David F. Chang, M.D., clinical professor, University of California, San Francisco.

Dr. Chang said he prefers a maximally dispersive OVD, such as Viscoat, in eyes at highest risk for corneal decompensation. Vitrax is also in this category, but is presently unavailable in the United States. He also pointed out that the study does not address the comparative performance of other modern OVDs, such as Healon5 (sodium hyaluronate 2.3%, AMO), DisCoVisc, and Amvisc Plus (sodium hyaluronate 1.6%, Bausch & Lomb, Rochester, N.Y.), all which persist in the eye longer than Healon.

Although the patients were randomized in the study, Richard S. Hoffman, M.D., associate clinical professor of ophthalmology, Casey Eye Institute, Oregon Health and Science University, Portland, Ore., said the number of patients in each group was small enough that if one group had several more eyes with denser cataracts, this could result in a higher percentage of endothelial cell loss.

“Similarly, a few cases with larger amounts of energy used would have the same effect,” said Dr. Hoffman.

Dr. Hoffman, who also mainly relies on Viscoat, said he hopes future research of this type might instead compare that OVD with others commonly used by U.S. surgeons.

Editors’ note: Dr. Colvard has financial interests with AMO (Santa Ana, Calif.). Dr. Modi has financial interests with Alcon (Fort Worth, Texas). Dr. Chang has financial interests with both AMO and Alcon. Dr. Hoffman has no financial interests related to his comments.

Contact Information

Chang: 650-948-9123, dceye@earthlink.net

Colvard: 818-906-2929, eyecolvard@earthlink.net

Hoffman: 541-687-2110, rshoffman@finemd.com

Modi: 845-454-1025, lasiknewyork@aol.com

Refrence:

1. Storr-Paulsen A, Norregaard JC, Farik G, and Tarnhoj J. Acta Ophthalmologica Scandinavica. 2007; 85(2):183-187.

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