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When considering the Boston type 1 keratoprosthesis as the evidence-based procedure of choice for managing cornea graft failure, superior visual outcomes must be weighed against greater risk of sight-threatening complications.
By Laird Harrison; Reviewed by Anthony J. Aldave, MD
Keratoprosthesis (KPro) implantation appears to result in similar or better outcomes than penetrating keratoplasty (PK) in patients who have had corneal graft failure, according to Anthony J. Aldave, MD.
Patients receiving the Boston type 1 keratoprosthesis (Massachusetts Eye and Ear Infirmary) enjoy a greater likelihood of improved visual acuity without a higher risk of postoperative glaucoma, Dr. Aldave and colleagues found.
Ã¢â¬ÅThe percentage of patients with a visual acuity of 20/200 or better 2 years following Kpro implantation is higher than in patients who have had repeat PK, although given the nature of the study we didnÃ¢â¬â¢t perform statistical analyses to determine if the difference between the groups was significant,Ã¢â¬Â said Dr. Aldave, professor of ophthalmology at the University of California, Los Angeles.
Patients with failed corneal grafts have two surgical options: another keratoplasty or a keratoprothesis, he noted.
Ã¢â¬ÅThere has been a lot of discussion regarding the optimal management of patients with repeat transplant failure,Ã¢â¬Â Dr. Aldave said.
To compare these approaches, Esen Akpek, MD, professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins University of Medicine, Baltimore, and colleagues including Dr. Aldave and others focused on the most common form of keratoplasty performed for corneal graft failure, PK, and the most commonly implanted keratoprosthesis, the Boston Type I.
This device consists of a PMMA front plate and optic, a PMMA or titanium back plate and a donut of donor corneal tissue sandwiched between them.
In reviewing the literature, Dr. Aldave and his colleagues could not find any controlled trials comparing outcomes of keratoprostheses with donor corneas in patients undergoing repeat transplantations.
They identified 45 reports of 26 non-randomized studies evaluating outcomes for patients undergoing repeat PKs after a history of failed corneal transplantation. The meta-analysis that they performed focused on the outcomes in 3,344 patients in 10 of these 26 studies.
The outcomes of repeat PK in these 10 studies was compared with the outcomes of 98 patients (104 eyes) with a prior history of graft failure who underwent keratoprosthesis surgery for the first time between January 2003 and December 2006 at five tertiary care referral centers.
Of these 98 patients, 31 had a history of only 1 previous keratoplasty. Primary outcome measures were visual acuity, repeat PK survival, keratoprosthesis retention, and the incidence of postoperative complications.
In regard to visual acuity, researchers estimated that following a repeat PK, patients had a 42% chance of achieving a corrected distance visual acuity (CDVA) of 20/200 or better 2 years after surgery, based on the 9 studies that reported on this outcome. By contrast, 57% eyes receiving the Boston keratoprosthesis maintained 20/200 CDVA 2 years after surgery.
In regard to graft survival following a repeat keratoplasty, researchers estimated that the percentage of grafts that were clear was 79% at 1 year, 67% at 2 years and 47% at 5 years. In comparison, the percentage of keratoprostheses retained at the same time points was 99% at 1 year, 95% at 2 years and 75% at 5 years.
In regard to postoperative complications, the researchers looked at the incidence of two that may occur following either procedure, glaucoma and infectious keratitis.
The proportion of patients developing glaucoma after repeat PK was 25%, with an average follow-up of 31 months. Infectious keratitis developed in 18% of eyes.
While the majority of eyes undergoing keratoprosthesis implantation already have glaucoma, making a comparison with the incidence of glaucoma development in eyes undergoing repeat PK problematic, a similar percentage of eyes, 28.8%, experienced an elevation in IOP by 3 years after keratoprosthesis implantation. At the same time point, infectious keratitis had been diagnosed in 2.9% of eyes.
Ã¢â¬ÅOne of the surprising things from the study was the incidence of complications following repeat keratoplasty,Ã¢â¬Â Dr. Aldave said.
Ã¢â¬ÅItÃ¢â¬â¢s known that progression of glaucoma is the most common cause of loss of vision following keratoprosthesis implantation,Ã¢â¬Â he added. Ã¢â¬ÅThis study indicates that it occurs in a significant percentage of eyes following repeat PK as well.Ã¢â¬Â
The published repeat PK results varied widely, which the researchers ascribed to the diversity of underlying diagnoses, follow-up times and clinical settings.
The results are in line with other pooled studies and large case studies, the researchers said. Three studies with high rates of 1-year PK failure were from India, where ocular surface disease rates are higher and the quality of donor tissue is more variable, they said.
On the other hand, one center, the Price Vision Group, had much better outcomes than the others, perhaps because their patients were healthier and their care more uniform, the researchers said.
They pointed out that centers performing a high number of grafts tend to report better outcomes.
The studies suggested that each subsequent regraft resulted in a higher likelihood of graft failure and worse visual prognosis.
In a separate study of long-term outcomes following Boston keratoprosthesis implantation for a variety of indications, not just repeat keratoplasty failure, Dr. Aldave and colleagues followed 74 Boston type I keratoprostheses for a mean of 82.8 months.
At baseline, CDVA was equal to or better than 20/200 in only 5% of eyes. At 4 years, that proportion rose to 57% and at 8 years it was 82%. Sixty-four percent of eyes that regained CDVA equal to or better than 20/200 after implantation maintained that level of acuity at the final follow-up.
As the most common cause of failure to obtain and to maintain this level of visual acuity was glaucoma, this finding points to the importance of proactive glaucoma management in patients with keratoprostheses, Dr. Aldave and colleagues concluded.
More research is needed on the long-term outcomes of the Boston keratoprosthesis, with prospective trials comparing the outcomes with those of repeat PK.
However, given the data available at this time, Dr. Aldave noted that the Boston keratoprosthesis is a viable alternative to repeat PK for the management of graft failure, with favorable comparative visual acuity, retention and complications outcomes.
Anthony J. Aldave, MD
This article was adapted from Dr. AldaveÃ¢â¬â¢s presentation at the 2017 meeting of the American Academy of Ophthalmology. Dr. Aldave is a consultant to Avellino Laboratories, ClearView Healthcare Partners, 5AM Ventures, Gore, Noveome Biotherapeutics, Shire, and Sun Ophthalmics, and has received grant support from the National Eye Institute.