We read with interest the recent study by Greenrod and associates assessing corneal graft outcomes from the United Kingdom (UK) transplant registry. We took particular note of the finding that endothelial keratoplasty (EK) survival was poorer in older donors aged over 75 years and in donors with baseline endothelial cell densities (ECD) less than 2400 cells/mm 2 . The impact of donor characteristics, including age and ECD, on EK survival has not been fully established, but this and other recent reports suggest the role may be significant.
EK survival outcomes reported by both Coster and associates from the Australia registry and Greenrod and associates from the UK registry were disappointing by comparison to survival outcomes from large, single-center EK series, many emanating from the United States (US). The authors of the registry studies have suggested several factors that may explain the discrepancy, including surgeon and center experience, socioeconomic patient factors, and discrepancy in donor material between countries. We would like to take the opportunity to further elaborate on this latter point.
We compared donor ages for corneal grafts in the UK (using data obtained from the UK registry) against published data from Australia (via the Australian registry) and the US (via the Eye Bank Association of America). The proportion of donors over age 70 years was 42% in the UK, 32% in Australia, and 18% in the US. While 50% of US donors were under 60 years, this was true of only 36% and 43% of UK and Australian donors, respectively.
Donor data specific for EK surgery were not available from the Australian and US publication sources, but from the UK registry the proportion of EK donors over 70 years was particularly high at 62%. EK donor characteristics from the UK registry closely resemble our own UK institution’s experience: out of 287 EK grafts, 63% have involved donors over 70 years of age. It is significant to note that donor ages in the UK have been increasing over the years, with a corresponding decline in ECD counts. At our center, mean donor ECD for EK surgery was only 2560 cells/mm 2 (median: 2550; range: 2200-3230), with 21% of donors less than 2400 cells/mm 2 as opposed to only 4% with a count over 3000 cells/mm 2 .
Given the evidence emerging about the influence of donor factors including age and ECD on EK survival, and in light of the variability in donor characteristics by country, we believe it is important that EK outcomes from surgical centers and international registries be interpreted with baseline donor characteristics in mind. Unfortunately, many studies on EK outcomes have hitherto failed to rigorously report donor characteristics, especially donor age. Until more robust evidence becomes available, and while eye bank practices remain variable, it is important that clinicians report their tissue characteristics and remain vigilant about the potential impact of these factors on their own outcomes and those emanating from different centers.