AlphaCor Artificial Cornea

Clinical Outcome

N Jirásková; P Rozsival; M Burova; M Kalfertova

Disclosures

Eye. 2011;25(9):1138-1146. 

In This Article

Discussion

In eyes with severely diseased corneas in which standard corneal transplantation has poor prognosis, an artificial cornea can provide good VA when successful. Keratoprosthesis surgery is carried out in very few centers, and devices design, surgical technique, and adjunctive therapies are evolving with experience.

AlphaCor artificial cornea was designed to address the need for an alternative to donor tissue, and to avoid the classic trial of sight-threatening KPro complications—progressive glaucoma, endophthalmitis, and retinal detachment.[28,29] It was intended to avoid reliance on donor tissue for its implantation while providing for reversibility to PK in the event of complications to minimize long-term risk to the eye.[2] AlphaCor design features include its flexibility and form (analogous to a small donor corneal graft) that allows a relatively non-invasive implantation procedure. The design of the optic, when associated with an opening in the covering tissues after completion of stage II surgery, produces an acceptable visual field and allows intraocular examination. The IPN between the core and skirt creates a permanent and very strong junction, preventing aqueous leakage.[3]

The appropriate selection of patients for AlphaCor implantation is crucial for success. There should be severe, debilitating corneal disease-causing blindness, with a poor chance of success from primary or repeated donor PK. The majority of patients undergoing AlphaCor Kpro implantation at our department had multiple prior failed grafts. Only three high-risk cases (one patient with OCP and two with bilateral serious alkali burn) received the device without prior transplant, but all three had history of multiple failed-donor PK in the other eye. AlphaCor performs best in a reasonably normal ocular environment. This includes eyelid health, a good tear film, and an absence of active inflammation. Generally, three broad classes of potential AlphaCor recipient could be identified: (1) those with poor prognosis from donor PK, but with good prognosis for AlphaCor implantation both for anatomical and functional outcomes; (2) those with a poor prognosis from donor PK and also a relatively poor or uncertain prognosis in terms of final vision with artificial cornea due to previous glaucomatous damage or macular disease, but with a good prognosis for an anatomically satisfactory outcome without significant complications; (3) those with a greater risk of significant complications affecting not only final vision but also reducing the chance of successful long-term device retention. However, those categories are not strictly divided and as it was mentioned previously, the indications have been evolving with experience. History of HSV infection was previously considered as an exclusion factor for AlphaCor surgery, but new data proved that HSV is not a risk factor for melts.[2] Ocular cicatrical pemphigoid is considered as a relative contraindication for AlphaCor implantation (category 3), but in our series, the patient with OCP has reached very good long-term outcomes with optimization of patient's condition before AlphaCor surgery (repeated electrolysis of trichiasis, and fornix, and lid reconstruction surgery).

The lamellar surgical procedure has been refined such that stage I surgery takes less than 1 h and does not require adjunctive tissue or devices. In our series there was no need to perform a full Gunderson flap or to use buccal mucosa, and no serious perioperative complications occurred during the stage I surgery. Cataract surgery was performed concurrently with AlphaCor implantation in two cases also without any complications. An earlier study by Hicks et al[2] reported higher occurrence of perioperative complications (19.9%). An uneventful phacoemulsification with PC IOL implantation was performed in one eye with cataract progression with very good postoperative outcomes (Figures 3 and 4).

In our series, three patients (20%) experienced penetrating injury after AlphaCor implantation, despite they were strongly educated about the necessity of long-term protection of the operated eye. This high rate is rather alarming. We believe that there are patients with 'higher inclination' to trauma, and not even previous disaster injury can teach them to protect themselves.

AlphaCor does not seem to exacerbate elevation of IOP. Glaucoma has been reported a common complication of rigid KPro,[28] commonly requiring drainage devices and frequently resulting in loss of vision. AlphaCor retention is not affected by glaucoma or the presence of drainage devices, and AlphaCor implantation does not seem to worsen glaucoma control.[2] In this series, only one case of acute elevation of IOP was observed at 6 days after stage I, and was satisfactorily treated using cyclocryocoagulation.

The most common postoperative complication was stromal melting adjacent or anterior to the device skirt. This was observed in nine cases (60%), and culminated in device explantation and replacement with donor graft in five eyes (33%). An important aspect of the response of the host tissue after KPro implantation is the production of enzymes. If this response is extensive, an increased risk of tissue melting and KPro loosening or extrusion would be expected. Coassin et al[30] have noted strong expression of various inflammatory cytokines, and only a few inflammatory cells in the three AlphaCor devices explanted because of corneal melting during the late postoperative period. They proposed that these cytokines were expressed by the keratocytes themselves because it is well known that the injured epithelial cells can stimulate fibroblast myodifferentiation of the keratocytes through inflammatory cytokines. On the basis of these observations, they speculated that an epithelial defect overlying the skirt portion of a well-biointegrated device can initiate the cascade of events and can lead to a corneal melt and device extrusion. Not only proper biointegration of the artificial material in the corneal stroma but also achievement of complete and stable epithelization of the entire device is necessary for long-term retention of the AlphaCor KPro in situ.

Alternatives to AlphaCor implantation include other KPro, repeated donor PK, and more recent forms of ocular surface transplantation. Other KPro in use today include the Boston KPro, Osteo-Odonto-Keratoprosthesis (OOKP), KeraKlear KPro, and Pintucci Kpro—the last, however, being rarely used today. Indications for OOKP and Pintucci implantation are similar: namely, severe end-stage ocular surface disorders. The Boston and KeraKlear KPros (like the AlphaCor) are considered a treatment option for repeated graft failure, herpetic keratitis, ocular burns (acid and alkali), OCP, Stevens–Johnson syndrome, and other autoimmune diseases. Although direct comparison of all these devices is inappropriate because of variations in disease indications and severity, several articles reporting results with these KPros have been published.[28,29,31–36] In assessing these devices, visual outcomes and anatomic success in terms of KPro retention are especially important. Results with OOKP are promising, with good device retention, good visual performance, and relative paucity of device-related complications,[35,36] but it is relatively complicated 2(3)-stage procedure insisting return visits to operating room with delayed visual recovery. The Boston KPro is a one-stage procedure but usually requires a new corneal carrier graft for assembly of the polymethacrylate device. Interest in the Boston KPro has grown significantly and is currently the most commonly implanted KPro in the United States.[37] A promising large multicenter Boston Type 1 study showed that at mean follow-up of 8.5 (0.03–24) months the retention rate was 95%.[31] Eighty-three percent of cases were performed for graft rejection, chemical burn, or aphakic/pseudophakic bulous keratopathy, indications that differ from OOKP or Pintucci KPros series. Of these patients, 22.6% achieved vision of 20/40 or better. Bacterial endophthalmitis was not reported in this series, however it was reported in other studies.[33] The KeraKlear KPro is a new foldable and injectable single-piece artificial cornea with no back plate or locking ring designed to create a clear window in an opacified cornea.[37] The steps of the procedure are outlined for both full-thickness and lamellar technologies, but according to our experience with this KPro, the lamellar technique (non-penetrating) is the only one full-proof and safe method.

In conclusion, in our series, patients typically had complex ocular histories with multiple pathologies. Their corneal blindness was not treatable successfully by means of standard dPK implantation, and implantation of an artificial cornea was the only chance for them to improve vision. Although BCVA improved in the majority of patients after implantation, the incidence of complications was relatively high, especially in long-term follow-up (2 and more years after implantation). The most serious complications were stromal melts and optic deposition or surface spoilation. In our series, we have also observed three cases of trauma (device-unrelated complication). Each case has required individual assessment and management. Patient's compliance is of high importance in evaluating any prospective case for AlphaCor implantation. As with all Kpros, ongoing vigilance in follow-up is essential, and care of these patients is challenging and time consuming.

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