sajjanshenoy
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12.10.05 (3 years ago)
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Mushroom Keratoplasty
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Massimo Busin, MD, clinical associate professor at Louisiana State University Health Science Center in New Orleans, has recently developed a novel technique for transplanting corneal tissue that combines a large lamellar graft with a smaller penetrating central graft, creating a mushroom-shaped area of donor tissue. The procedure works well for patients with full-thickness opacities but a healthy endothelium, such as those with stromal dystrophies.
According to Dr. Busin, mushroom keratoplasty has several advantages over other options. “With this procedure, you get a clear visual axis because you remove the full thickness of the cornea in the central 5 to 6 mm—the optical zone—and the small diameter results in a lower rejection rate. However, doing just a small-diameter, full-thickness transplant would cause distortion and irregular astigmatism.
“The advantage of a large graft on the front is that large grafts are known to have better refractive results,” he says. “But if you do a full-thickness large graft, the risk of rejection is higher. By combining the anterior large graft with the posterior small graft, you retain the advantages of both procedures and eliminate the disadvantages.”
Dr. Busin says that he begins the procedure by removing the mushroom “head and stem” sections of the patient’s cornea. “First, I make a partial thickness 9-mm incision, about 200-µm deep, using a trephine,” he says. “I do the dissection of the lamellae by hand because the resulting surface will be outside of the visual axis. This creates a slightly rougher interface, which allows more wound healing to take place, creating a stronger bond between the tissues. Then I punch out the central part of the stromal and endothelial tissue completely, leaving a central hole of 5 or 6 mm to match the posterior graft.”
Next, Dr. Busin splits the donor cornea into anterior and posterior lamellae using a microkeratome. “I make the top slice of the donor cornea section as wide as possible,” he explains. “Then I take it and punch it to size using the 9-mm trephine. I use another trephine to punch out a 5- or 6-mm central graft from the posterior lamella.”
Dr. Busin places the “mushroom stem” in the central hole of the recipient’s stromal bed with no sutures. He then places the superficial lamellar flap in the corresponding hole in the recipient’s cornea, fixing it with a running 10-0 nylon suture. After surgery, the patient uses antibiotic and steroid drops for two weeks, tapering over a period of about three months; then the sutures can be removed.
Dr. Busin says he’s done the procedure about 40 times, including one lattice dystrophy. In a case study reported in the July, 2005 issue of the American Journal of Ophthalmology
, the patient’s best corrected visual acuity improved from 20/60 preop to 20/20 at six months postoperatively.
Dr. Busin points out another advantage of this procedure: The small diameter of the posterior section of the graft may prevent the need for further surgery even if the immune system rejects the donor endothelial cells. “The normal endothelial cell count is about 3,000 cells per square millimeter,” he explains. “If you remove the central 5 mm of endothelial lamellae, you’re actually removing less than 20 percent of the endothelium. These cells don’t replicate, but they move along the basement membrane from areas of higher density to areas of lower density. If the donor endothelial cells die, the recipient’s healthy cells may spread over the graft and revitalize it. The density would still be sufficient to keep the cornea clear.”
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