Looking to long-range keratoprosthesis outcomes

Chicago-Findings from a single-surgeon consecutive series including 97 eyes with up to 12 years of follow-up provide realistic insights for corneal surgeons about long-term outcomes after implantation of the Boston keratoprosthesis type 1 (“Boston KPro”; Massachusetts Eye and Ear Infirmary).

The information-which included analyses of visual acuity results, device retention rates, and complications associated with the permanent keratoprosthesis-was presented by Anthony J. Aldave, MD, at Cornea 2016.

Dr. Aldave noted that long-term results of the Boston KPro was the subject of a retrospective study published about 2 years ago [Ophthalmology. 2014;12:2159-2164].

“I was fortunate to be part of that group and consider it a very important publication,” said Dr. Aldave, professor of ophthalmology, The Stein Eye Institute, University of California, Los Angeles.

“However, the data are from a multicenter cohort and reflect many different surgeons with different indications for surgery and different postoperative management regimens,” he said. “I wanted to look at the long-term outcomes of the Boston Kpro in my experience as a single surgeon.”

His series included 93 patients and encompassed 120 implantation procedures performed between May 2004 and May 2011. The average follow-up was just under 5 years.

The most common indication for the Boston Kpro procedure was failed corneal transplant (57%) followed by Stevens Johnson syndrome (SJS; 11%) and chemical injury (10%).

“In almost every KPro series, failed corneal transplant is the most common indication, and we know that SJS and chemical injury are associated with a more guarded long-term prognosis,” Dr. Aldave said.

Significant visual improvement

Significant visual improvement

The analysis of functional outcomes showed that prior to the Boston KPro, about 6% of eyes achieved 20/200 or better corrected distance visual acuity (CDVA) while 88% had CDVA of count fingers or worse. At 1 year, about two-thirds of eyes had CDVA of 20/200 or better, and looking at outcomes from 5 years and later, the rate consistently remained above 60%.

A Kaplan-Meier survival analysis showed that at 10 years, about 70% of eyes that had retained the Boston KPro would have 20/200 or better CDVA.

In another analysis, Dr. Aldave compared patients’ best ever CDVA with their final vision and found that about three-fourths of eyes had final vision that was ±3 lines of their best ever functional outcome.

He explained this analysis was conducted considering situations where a patient’s vision improves remarkably after vision but subsequently decreases because of a complication, such as progression of glaucoma.

“These patients may still have better vision after surgery than before even though they have lost vision postoperatively,” he said.

Reasonable retention rates

Reasonable retention rates

Of the 97 eyes in the series, 28 (29%) had a device removed, while 39 (32%) of the total 120 implanted devices were removed. At last available follow-up, 84% of the 97 eyes still had a keratoprosthesis. Mean time to failure approached 3 years, and based on a Kaplan-Meier survival curve analysis, Dr. Aldave noted that most retention failures occurred fairly early after surgery.

The retention failure rate was influenced by indication for surgery. Eyes that had failed corneal transplantation had a significantly lower retention failure rate compared with all other eyes in the series whereas eyes with SJS had a significantly higher retention failure rate when compared to eyes operated on for all other indications.

“Interestingly, eyes with chemical injury or mucous membrane pemphigoid, which traditionally are considered to be associated with a higher risk of retention failure, did not have a significantly higher retention failure rate than eyes with other indications,” Dr. Aldave observed.

Retention failure was also influenced by the development of complications and was significantly increased when eyes developed corneal stromal necrosis or infectious keratitis.

Highlighting a role for Boston KPro implantation after corneal graft failure, Dr. Aldave compared its retention outcomes with rates of repeat graft failure.

“The chance of having a clear graft at 4 years for a patient who has a repeat penetrating keratoplasty is about 30% and decreases to about 20% after a third or fourth penetrating keratoplasty procedure,” he said. “At 4 years after Boston KPro implantation, the patient would have about an 80% chance of device retention. In my mind, there is no contest between the two.”

Complications

Complications

Retroprosthetic membrane formation was the most common complication in the series, occurring in around 60% of eyes. While that rate is higher than has been reported in other series, Dr. Aldave reminded attendees that his cohort has longer follow-up.

The next most common complications were persist epithelial defect (41%), sterile corneal stromal necrosis (26%), and elevated IOP >25 mm Hg (23%). Only about one-third of the latter patients, however, required glaucoma surgery.

Dr. Aldave also highlighted that in his series with follow-up extending beyond 10 years, there was just a single case of endophthalmitis.

Looking at time trends for complication rates, his analyses showed infectious keratitis and sterile vitritis occurred most often in the second year after surgery. The incidence for all other types of complications was highest in the first postoperative year.

In addition, his analysis showed that excluding the single case of endophthalmitis, the incidence of each type of postoperative complication decreased significantly over the first 10 years after surgery.

“This bodes well for even longer-term outcomes with the Boston Kpro type 1,” Dr. Aldave concluded.