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Corneal prosthesis can treat patients contraindicated for human graft, surgeon says
The artificial cornea is implanted in a two-step procedure.
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The AlphaCor artificial cornea may be a feasible alternative to human corneal grafts in high-risk patients who would fare poorly with donor implants, according to a surgeon familiar with the device.
“The ideal patient for a keratoprosthetic has gone through numerous surgeries, has had extensive scarring and vascularization from injuries or progressive disease or has had multiple rejections of a corneal transplant from a human donor, and is now unsuitable for repeat human grafting,” said Arun C. Gulani, MD, director of refractive surgery and chief of corneal and external disease at the University of Florida in Jacksonville.
Dr. Gulani said he has implanted all three types of AlphaCor (Argus Biomedical Pty Ltd) soft artificial corneas: phakic, pseudophakic and aphakic.
“Data from clinical trials by Celia Hicks et al have shown that the artificial cornea can treat some high-risk indications more effectively than the human graft,” Dr. Gulani said.
Clinical trials sponsored by the Lions Eye Institute in Nedlands, Australia have so far produced follow-up data to 5 years. Postoperative visual acuity ranged from light perception to 20/20 (–2), according to a study published in Eye. There was a low incidence of complications traditionally associated with keratoprostheses, the study authors said.
The AlphaCor was approved by the Food and Drug Administration in late 2002. Since the U.S. rollout in June 2003, more than 25 devices have been implanted in U.S. patients. Argus Biomedical received Medicare pass-through in July 2003.
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Graft design
Dr. Gulani attributed the successful study outcomes to the “unique” design of the AlphaCor.
The graft is a one-piece, hydrogel poly (2-hydroxyethylmethacrylate) (PHEMA) convex disc. The disc is composed of a “core” and “skirt.” The outer skirt, an opaque high-water-content PHEMA sponge, provides biointegration with human tissue.
“This sponge allows the patient’s own tissue to grow into it and secure it in place,” Dr. Gulani said.
Between the sponge and the core is an interpenetrating polymer network (IPN). The IPN is a molecular bond that prevents the downgrowth of cells around the optic, which could potentially develop into retroprosthetic membranes.
The central core of the optic disc acts as the lens.
“Transparent PHEMA gel provides a clear optic with a refractive power in situ similar to that of the human cornea, allowing visual potential to be restored,” said Jim McCollum, CEO of Argus Biomedical.
Implantation
Implantation of the AlphaCor is performed in a two-stage procedure carried out over 3 months.
“The first stage involves placing the artificial cornea in a lamellar corneal pocket, covered by a Gunderson’s flap. The second stage, usually 3 months after, consists of removal of the Gunderson’s flap and anterior corneal layer to reveal the optic surface of the artificial cornea,” Dr. Gulani said.
Dr. Gulani said he envisions adding a third stage to this procedure, which would allow for resculpting the artificial cornea with the excimer laser for an optimum refractive result. He also devised a task-specific set of instruments and modified the procedure.
Surgical stage 1
Stage 1 of the procedure begins with the creation of a Gunderson’s conjunctival flap. Dr. Gulani uses Westcott scissors and concentric forceps to cut and pull away the superior fornix from the surgical site.
A narrow scleral rim is created with a 300-µm preset knife that Dr. Gulani designed specifically for the procedure.
“This knife enables surgeons to make a unique scleral curve in a single continuous movement,” he said.
After creating a scleral rim, he creates a 180° superior flap with a “single unzipping motion” by using a slit knife. With the slit knife, he enters the cornea at a horizontal depth of 300 µm.
“At the floor of the sclerocorneal flap, I form a small, intralamellar pocket,” he said.
Dr. Gulani then uses a blunt, multidirectional corneal dissector that he designed.
“I create a uniplanar resistance-guided dissection that forms a firm pocket in the cornea,” he said.
He then injects viscoelastic through a self-sealing peripheral paracentesis.
Because AlphaCor can be implanted in phakic, aphakic or pseudophakic patients, Dr. Gulani uses a slightly different approach for each patient.
“For an aphakic patient with a protrusive vitreous, I perform a closed-system vitrectomy and then inject the viscoelastic in a self-sealing peripheral paracentesis,” he said.
After viscoelastic injection, Dr. Gulani creates a central posterior trephination with a low-profile 3-mm trephine, and removes the corneal button. He inserts the AlphaCor corneal prosthetic with a specially designed holding forceps, which achieves the dual function of determining the adequacy of the artificial cornea as well as securely inserting the AlphaCor in place.
Dr. Gulani then uses a single mattress suture to prevent the prosthetic from shifting superiorly. He uses the needle he designed (Surgical Specialties). Finally, the sclerocorneal pocket is closed and sealed with 10-0 nylon sutures.
Surgical stage 2
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More information on the AlphaCor artificial cornea from Argus Biomedical Pty Ltd is available through the company’s ArgusConnect program. Information is available about the procedure, patient selection criteria and postop management regimens. ArgusConnect puts surgeons in touch with an international network of corneal surgeons, who host guest surgery visits, relay information on clinical data and teach surgical techniques to physicians interested in the AlphaCor. For more information, visit Argus Biomedical on the Web at www.argusbiomedical.com or e-mail info@argusbiomedical.com. |
Surgeons must wait at least 3 months to perform the second stage of surgery, in the office or operating room. Such a duration is necessary to allow bioadhesion of the artificial cornea to human tissue, Dr. Gulani said.
In stage 2, the central portion of the tissue that covers the AlphaCor optic, comprising the conjunctival flap and the anterior roof of the corneal pocket, is removed.
Removal of this tissue exposes the front optical surface of the artificial cornea. At this point, a patient should see through the artificial cornea, but may need refractive correction to achieve the best ability of that eye, he said.
Dr. Gulani said he would also like to see the skirt portion match the color of the patient’s iris, and he would like to see a whiter optical zone.
“I commend Celia Hicks, MD, and Geoffrey Crawford, MD, at the Lions Eye Institute of Western Australia, for their extensive work in this field,” Dr. Gulani said.
For Your Information:
- Arun C. Gulani, MD, is director of refractive surgery and chief of cornea and external disease, Department of Ophthalmology, University of Florida-Jacksonville. He can be reached at 580 West 8th St., Jacksonville, FL 32209-6561; (904) 244-9393; fax: (904) 244-9394; e-mail: arungulani@aol.com. Dr. Gulani has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Argus Biomedical Pty Ltd., makers of the AlphaCor Artificial Cornea, can be reached at Lion’s Eye Institute Building, 2 Verdun Street, Nedlands, Perth, Western Australia 6009; (61) 8-9381-0834; fax: (61) 8-9381-0759; Web site: www.argusbiomedical.com.
Reference:
- Hicks CR, Crawford GJ, et al. Corneal replacement using a synthetic hydrogel cornea, AlphaCor: device, preliminary outcomes and complications. Eye.2003;17:385-392.