Evolving techniques enhance results with keratoprosthesis

July 15, 2005

Washington, DC—Accruing experience with the AlphaCor (Argus Biomedical) synthetic keratoprosthesis has led to the identification of risk factors for complications along with the development of protective procedures that are enabling better outcomes, said R. Doyle Stulting, MD, PhD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

"With an evolving surgical technique and developments in postoperative management, complication rates have fallen and 1-year survival rates are favorable. However, long-term data must continue to be collected for better understanding of the benefits of this technology, its limitations, and where it fits into our practices with relation to human tissue donor grafts," said Dr. Stulting, professor of ophthalmology, Emory University, Atlanta.

The AlphaCor is a 7-mm diameter, one-piece, non-rigid hydrogel synthetic cornea indicated for use in patients considered to be at high risk for penetrating keratoplasty (PK).

Speaking on behalf of the AlphaCor Scientific Advisory Board, Dr. Stulting reported results from 251 patient-years of experience based on data collected for 239 devices implanted by 69 surgeons worldwide. About two-thirds of the procedures were performed in the United States. About 90% were done for on-label indications.

The patients in the AlphaCor cohort are predominantly Caucasian (72%) and male (62%). They range in age from 1 to 90 years with a mean of 58 years. About half of the subjects had glaucoma, and 17% had diabetes. About 60% of the cohort were pseudophakic and 18% were aphakic. Bullous keratopathy was the most common corneal pathology (35%). The mean number of failed grafts prior to AlphaCor implantation was 2.4 (range, 0 to 13). Mean follow-up for the patients was 12.6 months, with a range of 0.5 months to 6.5 years.

Preoperatively, best-corrected visual acuity (BCVA) ranged from 20/200 to light perception, with a mean of hand motion. BCVA postoperatively ranged from 20/20 to light perception, and overall, AlphaCor keratoprosthesis implantation was associated with a mean gain of 2 lines of BCVA.

"In many eyes, visual potential was limited by preexisting macular disease or significant glaucomatous damage," Dr. Stulting observed.

Survival rates at 1 and 2 years, considering only eyes receiving the device for an on-label indication and treated with medroxyprogesterone (MPG) postoperatively, were 82% and 63%, respectively. Considering 42 cases in the AlphaCor series that had ≤four prior failed grafts and were treated with MPG, the 1-year survival rate was 84%.

"That latter statistic compares favorably with results reported by the Australian Corneal Graft Registry that show a 46% 1-year survival rate after fifth and subsequent human donor PKs," Dr. Stulting said.

Poor primary biointegration occurred in six (2.5%) cases, and aqueous leakage was noted after the second surgical stage in these cases.

"Imaging performed in some eyes suggested a fluid tract, poor apposition, or an overly large pocket. This experience suggests that imaging should be performed prior to the second stage of surgery," Dr. Stulting said.

The most common complication in the series was stromal melting. However, its prevalence fell over time from 83% among 22 eyes in the premarket trial treated for an off-label indication without MPG treatment to 12.7% among 142 eyes treated on-label with MPG in the post-trial experience.