Equine corneal transplants' success rate growing - DVM
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Equine corneal transplants' success rate growing
Better technology, pharmacology needed to reduce tissue rejection, expert says


"We need to educate other practitioners — which this article will help to do — to understand that the horse's eye heals well. It's just that we vets have had to learn, and are learning how to help it heal, rather than slow the healing process. I'm never satisfied. I didn't accept the idea, the veterinary dogma of the recent past, that the horse eye heals poorly," Brooks says.

"At the University of Florida, our team decided to collect data, to do projects to learn how to help the eye heal, and the corneal transplantation is the result. Before we started doing transplants, we really didn't understand some of these diseases."

The main reason the group did corneal transplants was for stromal abscesses, which are seen frequently. "Before we started doing surgery, we didn't get most of those better. If we got 50 percent of them better, I'd be surprised," Brooks explains. "For one thing, we didn't know what was causing them. Because we didn't know the cause, we didn't know how to treat them. Most of the time we were treating the wrong disease."

In 1998, Brooks and colleagues at the University of Florida decided that if they had to treat a horse the way it had been treated in the past, it was not going to get better.

"I told the owners that we need to do surgery on these and try and figure out how to treat them better," says Brooks. "They did it. It worked. They learned about the cause, which in the case of most stromal abscesses was fungal infection. As they started doing these PKs, they unfortunately removed the normal tissue as well. So then they began to do PLKs and DLEKs, leaving the normal tissue, which speeds up healing, and removing only the damaged part.

"So if we're able to do the PLK or DLEK, the healing rate is dramatically faster compared to the PK," Brooks says. The success rate is greater than 90 percent.

"Because veterinarians are doing corneal transplants in infected cornea, with blood vessels, they're having 100 percent rejection of the graft, which means it doesn't stay clear. So if I put in a 6 mm diameter corneal transplant in a horse, if everything works perfectly, I'm going to get a 6 mm scar," Brooks explains.

"In the past, we were removing the eyes. With time, within about six months to a year, the 6 mm scar pretty much disappears, so the eyes were quite well healed. Regardless of the 'rejection,' the horses still are able to see.

"However, I'm not satisfied," Brooks says.

So research begins this summer to determine how to stop rejection. The only limits are time and grant funding.

There's room for significant improvement, Brooks says. Veterinary ophthalmologists are doing mostly low-technology surgery, he says. They have operating microscopes, but not all the equipment that physicians use for human corneal transplant surgeries.

"If we get a little better technology, that'll help," says Brooks. "Better pharmacology, I think, will help. We need better drugs in order to help prevent the rejection."

Rejection "probably is due to some chemicals (e.g., cytokines) being released in the tissue, and we've got to find out what they are. If so, we can turn them off, and then we'll be able to improve our results, no question," Brooks believes.

Physicians sometimes operate on patients who have eye diseases similar to the horse. "In human ophthalmology terms, all the cases that we do in horses are considered at high risk for rejection. There are blood vessels there," Brooks explains.

The difference? Physicians often perform a second surgery to remove scar tissue. Veterinarians don't have that option with equine patients.

"We veterinarians get one shot to help these horses. But, even with the scarring, some more than others, the horses can see, and obviously better than before or with no eyes. A lot better — dramatically better," Brooks says.

Ed Kane, PhD, is a Seattle author, researcher and consultant in animal nutrition, physiology and veterinary medicine, with a background in horses, pets and livestock.


Source: DVM360 MAGAZINE,
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