Irradiated sterile cornea holds promise

February 22, 2012

The promise and advantages offered by a newly developed, irradiated sterile cornea (VisionGraft, Tissue Banks International) for performing lamellar and other non-endothelial surgical procedures are great, according to Yassine J. Daoud, MD.

Baltimore-The promise and advantages offered by a newly developed, irradiated sterile cornea (VisionGraft, Tissue Banks International) for performing lamellar and other non-endothelial surgical procedures are great, according to Yassine J. Daoud, MD.

“The sterile cornea is a very promising technique. It has the potential to increase the supply of transplantable corneas,” said Dr. Daoud, assistant professor of ophthalmology, Johns Hopkins University School of Medicine, Wilmer Eye Institute, Baltimore. “One of the great things about the sterile cornea is the immediate access in emergencies and in remote areas.

“I have actually had two episodes where I didn’t have to contact the tissue bank, and just grabbed the corneas off the shelf and used them,” he added.

Corneal transplantation is the most successful and the most common form of tissue transplant surgery, Dr. Daoud noted. In the United States, about 50,000 corneal transplants are performed, and the same amount is completed overseas annually.

According to Dr. Daoud, surgeons are still faced with many challenges in the arena of corneal transplantation. Eight million to 10 million people are cornea blind, and about 5 million could undergo transplantation, he noted.

“But currently, we’re only [performing transplants for] about 1% of those who actually need transplantation,” he said.

Another challenge is that in the United States, about 20% to 25% of the corneas that are donated are actually discarded. In other countries, this discard rate can be as high as 75%. The reasons that make discarding this tissue necessary can include the following factors:

Unhealthy endothelium.

Cause of death is not known in a timely manner.

Surplus days, in which there are many donors but not enough transplants done and the tissue expires.

Positive serology.

To break it down further, Dr. Daoud said, of the 82,000 corneas donated each year, 23,000 are discarded. In addition, surgeons overseas and in remote areas have experienced a shortage of fresh corneal tissue for corneal transplants. The primary cause of this is the short shelf life of these transplants, which is 1 to 2 weeks.

“This has all brought us in search of a new delivery system for the cornea, which is the sterile cornea,” he said. “The sterile cornea is harvested in the same way any other cornea is harvested. But it is irradiated in a manner similar to what has been done with sclera and bone for the past 20 years. This confers stability onto the cornea and brings much less risk for disease transmission.”

Advantages of the sterile cornea include:

It can be stored for more than 1 year.

There is less risk of disease transmission (bacterial, viral, and fungal).

It can be precut for various applications.

It can be kept in stock in the operating room for emergency situations.

It is packaged for easy recognition and aseptic delivery at surgery.

It is effective for other applications, including glaucoma shunt coverage.

It exhibits ease of surgical use, easy-to-manipulate suture.

It has clarity of material.

Dr. Daoud highlighted the outcomes from the first 150 transplants used in several leading surgical centers in the United States and abroad. Respondents included surgeons from the Jules Stein Eye Institute, Los Angeles; Massachusetts Eye and Ear Institute, Boston; University of Rochester Medical Center, Rochester, NY; and the Wilmer Eye Institute.

“We sent a 1-page survey to surgeons who have used this cornea to find out how the cornea handled and what the intraoperative and postoperative outcomes were in these cases,” he explained.

Applications for the sterile cornea included keratoprosthesis, glaucoma patch graft, and emergency patch graft. There has been some use also as a skirt for keratoprosthesis, Dr. Daoud noted. The majority (65%) were used as glaucoma patch grafts, 14% as corneal patch grafts, 11% in automated lamellar keratoplasty, and 10% for keratoprosthesis. Primary diagnoses included traumatic corneal perforation, glaucoma patch, corneal scar, scleral melt from mitomycin C toxicity, and failure of initial and repeat corneal graft.

All respondents rated the sterile cornea favorably, he said. Most gave it 3.6 points and above on a scale of 1 (fair) to 4 (very good). For example, respondents rated the ease of use an average of 3.78 of 4, clarity an average of 3.64, thickness 3.68, tensile strength 3.62, and suturing 3.68.

There were no reports of postoperative infections or rejection. Adverse reports included four cornea melts, but all of these occurred in patients with previous cornea melt. One instance of leaking sutures was also reported.

Ratings for epithelialization (3.35 of 4), biological incorporation (3.38), and clarity (3.45) were all very good.

Dr. Daoud cautioned that the follow-up of transplants is short in these patients and ranged from 12 to 16 months. Respondents have noted that there have been no transplant rejections so far, but further studies are needed, he said.

“Longer follow-up is really needed to determine the incidence of de-epithelialization and clarity,” he said. “We are in the process of collecting reports and data from collaborators, and plan to compare standard lamellar with sterile cornea lamellar procedures.

“We are particularly interested in long-term outcomes, clarity, and adverse reactions,” Dr. Daoud concluded. “We know that the sterile cornea is very promising for non-endothelial cornea transplants, such as deep anterior lamellar keratoplasty for the treatment of keratoconus. We are investigating whether it may be used as a replacement for [corneal storage medium]-stored cornea in penetrating keratoplasty.”

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