Post-op cell density for predicting graft failure

Low post-op counts may bode poorly

Low six-month cell counts may indicate PK graft failure
Source: Jonathan H. Lass, M.D.

Patients’ endothelial cell counts at the six-month post-corneal transplant mark is a better indicator of subsequent graft failure caused by endothelial decompensation than the pre-procedure donor cell count, according to Jonathan H. Lass, M.D., Charles I. Thomas professor and chairman, department of ophthalmology and visual sciences, Case Western Reserve University, Cleveland, and director, University Hospital’s Eye Institute, Cleveland. Results, published in the January issue of Archives of Ophthalmology, indicate that those with an endothelial cell count density of 1,700 cells per mm2 at the six-month mark were more than six times more likely to suffer graft failure than recipients with counts of 2,500 cells per mm2 or higher.
This recent investigation was an outgrowth of a larger study. “The primary point of the study was to look at the age of the donor corneas to see if that had any impact on the survival of transplants after penetrating keratoplasty for conditions where the endothelium failed,” Dr. Lass said. In this initial portion of the study investigators found that the age of the donor was not a factor in graft success. “Approximately half of the grafts were from donors over age 65 up to 75 and the other half were under age 65,” Dr. Lass said. “Both groups had 86% survival at five years.”
An accompanying paper looking at cell loss in the two groups showed that both lost quite a number of cells. “The younger group lost 69% at five years, whereas the older group lost 75%,” Dr. Lass said. “It was statistically significant but this was not reflected in a difference in graft failure.”
Investigators are following these patients, whose grafts have survived, for another five years to see if the difference in cell loss could ultimately be reflected in a higher percentage of graft failures. They are now looking at other factors that influence graft success and cell loss.

Evaluating cell counts

In one subset of this corneal donor study, investigators have been keying in on endothelial cell density after penetrating keratoplasty as a possible predictive factor for graft failure. “In the eye banking community surgeons have always felt that the higher the cell count at baseline in the donor, the more successful in terms of graft success in the long term,” Dr. Lass said. The thinking was that graft success would come with younger donors because they tend to have higher cell counts. However, the initial study showed that that did not make a difference.
Included in this latest study were 17 grafts that failed due to endothelial decompensation and 483 grafts that did not fail. Investigators found that the five-year cumulative incidence of failure was 13% for those who at the six-month mark had an endothelial cell count of less than 1,700 cells per mm2. Meanwhile, for the 137 participants with a six-month count of 2,500 cells per mm2 or higher, there was just a 2% graft failure rate. At the five-year follow-up mark, of those whose grafts remained clear, 14% had counts below 500 cells per mm2.
“Looking at the baseline, a count in the low 2,000s was as good as a count in the over 3,000s in terms of graft success,” Dr. Lass said. “That suggests that it’s not so much the normal standards as how much damage occurs within the transplant and what happens post-operatively that is most important at 6 months.”

Clinical implications

Dr. Lass hopes that practitioners come away from the study with the understanding that it is the post-op cell count that is important for graft survival. “The main clinical implication is that the baseline cell count is OK as long as you’re within the normal EBBA [Eye Bank Association of America] criteria down to 2,000 cells per mm2,” he said. “There shouldn’t be a tremendous impetus toward getting the highest count (pre-op); we have to look at other factors during and after surgery that are probably more important.”
Given that six-month counts outside of studies are not the norm, practitioners must of course keep an eye out for potential graft failures. “If you see any indication that the graft is failing, any suggestion that the cornea has folds or an increase in thickness, get a cell count at that point because that’s clearly a cornea that’s having problems,” Dr. Lass said. “You’re going to have to watch them more closely because any kind of graft rejection episode is something that could tip the cornea over to fail.”
However, Dr. Lass stresses that a low cell count does not necessarily mean graft failure in an otherwise clear graft. “If a cornea should get out to five years, we found that about 20% had counts below 500. This is the largest group of grafts that we’ve seen that have low counts and are doing well,” he said. “If you get out that far and have a clear graft with a low count, that’s compatible with an excellent function graft.”

Editors’ note: Dr. Lass has no financial interests related to his comments.

Contact information

Lass: 216-368-4692, johnathan.lass@case.edu