Poorer tissue quality lowers utilization rate of pseudophakic donor corneas

Pseudophakic donor corneas tend to have poorer cell and tissue quality than phakic corneas, leading to lower rates of utilization, according to a recent analysis of the Singapore Eye Bank.

“A timely reassessment of the eye bank’s internal acceptance policy with regard to donor lens status exclusion criteria is required in order to address this issue and to ensure that utilization of all recovered corneas is optimized,” the researchers said. “Clear communication with surgeons is also important to ensure that corneas that fulfil the quality criteria for surgery should be accepted, regardless of donor lens status.”

Examining Singapore Eye Bank records for 2012 to 2017 revealed 986 corneas suitable for transplant and subsequent analysis. The vast majority (92 percent) of tissues were phakic, while the remaining 8 percent were classified as pseudophakic. Tissue quality was graded according to epithelial integrity, stromal clarity, and presence of pathology, among other parameters.

After adjusting for age, pseudophakic corneas showed a significantly lower average epithelial cell density (ECD; 2,327 vs 2,734 cells/mm₂; p<0.001) and clear area (7.0 vs 7.6 mm; p<0.001) than phakic tissues. In turn, pseudophakic tissues took significantly longer to be utilized than phakic counterparts (mean death to surgery interval, 7 vs 5.7 days; p=0.034). [PLoS One 2021;16:e0260523]

The Singapore Eye Bank requires a minimum ECD of 2,250 cells/mm² for elective optical penetrating keratoplasty. Eighty-nine percent of donated phakic tissues met this criterion, as opposed to only 53 percent of pseudophakic corneas (p<0.001).

Similarly, a minimum threshold of 2,500 cells/mm² is set for epithelial keratoplasty. For such a procedure, 77 percent of phakic corneas were found to be eligible, as compared with only 37 percent of pseudophakic tissues (p<0.001).

Aside from ECD, the stromal clear area was also an important factor in determining tissue quality. According to researchers, “an 8.0-

mm central clear zone was the minimum diameter that surgeons were comfortable with for majority of their patients.” Significantly more phakic tissues met this criterion than pseudophakic corneas (46 percent vs 17 percent; p<0.001).

Such clear differences in tissue quality led to discrepancies in utilization rates. While 83 percent of phakic tissues were eventually used for transplant over the entire study duration, only 58 percent of pseudophakic corneas were transplanted.

Conversely, in line with their lower utilization rate, a significantly higher percentage of pseudophakic tissues were frozen after 14 days of being unmatched (53 percent vs 20 percent; p<0.001).

“Our study reflects the difficulties small scale eye banks face in trying to obtain sufficient numbers of corneas to meet demand while ensuring efficient and optimal utilization of tissue,” the researchers said. “As this study was performed at a single eye bank in Singapore, the trends observed in this study may not reflect the general trend in other geographical locations where corneal transplants are performed.”