Alphacor (Coopervision Surgical Inc., Lake Forest, CA) is a one-piece, hydrophilic, synthetic cornea comprising a biointegratable, sponge skirt that surrounds a transparent optic with refractive power; the two regions are intimately joined at the molecular level.1,2 Biointegration has been confirmed in the animal model and after explantation from human subjects.3 The synthetic cornea is 7mm in total diameter, with a functional optic diameter of just over 4mm and a thickness of 0.5mm. Because the device is made of a hydrogel, once exposed to the ocular surface, it requires a wet environment and is at risk of depositions from some topical medications, similar to soft contact lenses. Two powers are available, one for aphakes and one for phakic or pseudophakic patients. The most common usage of the device is with regrafts and other vascularized corneas.
Alphacor represents an extra modality for the correction of corneal opacification in high-risk patients. Its use exists between human corneal donor surgery and the more traditional keratoprostheses such as the Cardona KPro and Osteo-odonto keratoprostheses. Outcomes data indicate that Alphacor performs better than human-donor-tissue keratoplasty in many situations, especially regrafts.
Alphacor is implanted in a staged surgery, separated by approximately 3 months (the period allowed for biointegration to occur within the skirt region4). During stage I, a half-thickness corneal pocket centered on the pupil and 8mm in diameter is created by lamellar dissection. The surgeon removes the central 3.5mm of the posterior lamella, either using a low-profile trephine or by opening the wound sufficiently to allow access for a skin punch. The device is centered over the posterior opening within the pocket, which is closed adjacent to the device by mattress sutures through the two lamellae. The surgeon then closes the entry incision, located 1.0 to 1.5mm posterior to the limbus, with 10–0 nylon sutures. Another option is to create a Gunderson flap, generally appropriate in cases with a compromised limbus and ocular surface. Patients take steroids and antibiotics postoperatively, generally topical only. Increased steroids perioperatively should be considered for patients with a particular risk for postoperative inflammation or reclosure of the posterior lamellar opening.5
PATIENT SELECTION AND MANAGEMENT
Regular review of the data has led to publications discussing particular associations of risk and protective factors with regard to patient outcomes. For example, stromal melting around the device was found to be associated with a prior history of herpes simplex virus,6 and topical medroxyprogesterone was reported to be protective.7 Risk factors for optic deposits and retroprosthetic membranes have also been identified,5,8 and evolving patient management in response to these factors appears to be reducing complication rates.9
Because approximately 200 Alphacor devices have been implanted to date, inferences from data must be regarded as preliminary, but probabilities of survival in situ to 1 and 2 years compare favorably with graft survival in patients with multiple prior graft failures and other high-risk groups.10 In patients whose grafts are at increased risk, such as those with glaucoma tubes in situ, current data seem to indicate that Alphacor may be superior to a cadaveric corneal transplant because of the higher risk of endothelial cell failure in eyes with a tube shunt device.
IMPLICATIONS FOR A PRACTICE
Surgeons must become accredited to use Alphacor by attending a course run by the manufacturer, which includes a wet lab and discussion of data from cases performed to date. Those whose practices involve lamellar procedures will find the Alphacor procedure straightforward; for others, a learning curve may be involved, and wet lab practice is recommended. Adjunctive procedures such as Gunderson flaps, if required, may be performed by a corneal surgeon. If a plastic surgeon assists, familiarization with the device's characteristics is helpful. Similarly, if glaucoma specialists assist with patient management, a familiarity with issues specific to Alphacor is useful (eg, topical medications to avoid and effects on postoperative IOP measurement).
Alphacor does not appear to be associated with an increased risk of postoperative glaucoma or worsening control of IOP. Thus far, postoperative shunts have not been required. If cataracts are present prior to Alphacor placement—and arguably in any phakic case—it is preferable to remove the cataract several months prior to Alphacor surgery if at all possible. In many cases where cataract surgery has been performed concurrently with Alphacor surgery, the reduced view has made surgery difficult and resulted in some retained soft-lens matter, both of which increase the risk of postoperative inflammation.11
The implantation of Alphacor can take from 40 minutes to more than 2 hours depending on the case; many eyes have undergone numerous previous procedures, and surgery can therefore be difficult. Patient scheduling should take this into account. Anonymous follow-up data are requested for the registry, from which analyses are performed and circulated to all surgeons, similar to a graft registry. Including patients in a registry (http://www.argusconnect.com) may require approval from an Institutional Review Board in some centers.
Alphacor patients require regular follow-up by someone familiar with the device and its management. Ideally, fellows or other colleagues likely to assist with care will be accredited and familiar with the recommended protocols. Surgeons should forewarn patients of the frequency of follow-up required (recommended to be at least every 3 months, even after 1 year6). Most patients will require only topical medications, rather than systemic steroids or other immunosuppressants, but ongoing compliance with topical medications is important and requires vigilance on the part of the ophthalmologist.Certain medications should be avoided after Alphacor surgery due to a risk of optic deposition;8 updated information can be obtained from the manufacturer's Web site.
Refractive correction after Alphacor can be challenging due to the tendency for the optic to be recessed compared with surrounding stroma/conjunctiva. The “ideal” contact lens for use postoperatively is not yet available. The authors' compromise has been to use the Purevision (Bausch & Lomb, Rochester, NY) silicone hydrogel lens for monthly disposable wear. We allow patients to wear a “special occasion” lens such as the Expressions cosmetic lenses (Coopervision Surgical Inc.). They provide excellent color and cosmesis when worn bilaterally by disguising the white sponge skirt, but they provide less oxygen permeability than is ideal for constant wear in these eyes.
Alphacor provides an option for those in whom a penetrating keratoplasty cannot be performed (Figure 1). The reversibility of Alphacor and its lack of invasive adjunctive procedures make the device appropriate in patients who have reasonable vision in their fellow eye, although the relative risk/benefit ratio requires careful discussion. The time taken for visual rehabilitation (several months) may be longer than that required for rigid, PMMA optic devices, but retention rates seem to be better with Alphacor. The avoidance of systemic immunosuppressants is an advantage compared with the regimes required for successful limbal stem cell surgery or the prevention of rejection in high-risk donor graft cases.
Continued data collection and analysis should help determine Alphacor's role more precisely. The implant cannot yet be recommended for children. For the best outcome, Alphacor patient management requires a team approach, often involving a cataract, glaucoma, plastic, and corneal specialist as well as a dedicated optometrist and interested nursing and technical staff. Voluntary data collection and involvement in discussion with other members of the Alphacor users' group is also beneficial to patients' outcomes.
Geoffrey J. Crawford, MD, is Associate Professor of Ophthalmology at the Lions Eye Institute and Centre for Ophthalmology and Visual Science, University of Western Australia, Nedlands, Australia. He holds a financial interest in Alphacor and Coopervision Surgical Inc. Dr. Crawford may be reached at +61 8 9381 0871; email@example.com.
David R. Hardten, MD, is Director of Refractive Surgery for Minnesota Eye Consultants in Minneapolis. He states that he holds no financial interest in the products and companies mentioned herein. Dr. Hardten may be reached at (612) 813-3632; firstname.lastname@example.org. Chirila TV, Vijayasekaran S, Horne R, et al. Interpenetrating polymer network (IPN) as a permanent joint between the elements of a new type of artificial cornea. J Biomed Mater Res. 1994;28:745-753.
2. Crawford GJ, Hicks CR, Lou X, et al. The Chirila keratoprosthesis: phase I human clinical trial. Ophthalmology. 2002;109:883-889.
3. Vijayasekaran S, Hicks CR, Chirila TV, et al. Histological evaluation during healing of hydrogel core-and-skirt keratoprostheses in the rabbit eye. Cornea. 1997;16:352-359.
4. Hicks CR, Crawford GJ. Indications and technique: AlphaCor artificial cornea. Tech Ophthalmol. 2003;1:151-155.
5. Hicks CR, Hamilton S. Retroprosthetic membranes in AlphaCor patients: risk factors and prevention. Cornea. In press.
6. Hicks C, Crawford GJ, Tan DT, et al. Outcomes of implantation of an artificial cornea, AlphaCor: effects of prior ocular herpes simplex infection. Cornea. 2002;21:685-690.
7. Hicks CR, Crawford GJ. Melting after keratoprosthesis implantation: the effects of medroxyprogesterone. Cornea. 2003;22:497-500.
8. Hicks CR, Chirila TV, Werner L, et al. Deposits in artificial corneas: risk factors and prevention Clin Exp Ophthalmol. 2004;32:185-191.
9. Hicks CR, Bulsara M, Crawford GJ, et al. The ArgusConnect data 2004. Abstract, 2004 Federated Scientific Session of the Cornea Society and the Eye Bank Association of America, New Orleans, October 2004.
10. Hicks CR, Crawford GJ, Tan DT, et al. AlphaCor cases: comparative outcomes. Cornea. 2003;22:583-590.
11. Eguchi H, Hicks CR, Crawford GJ, et al. Cataract surgery with the AlphaCor artificial cornea. J Cataract Refract Surg. 2004;30:1486-1491.