This study analyses the change in indications for corneal transplantation over a period of twenty years and shows a significant change in the spectrum of indications, which is due, among other things, to a rapid change in surgical techniques. The decline in penetrating keratoplasties is matching the overall global trend [22,23,24]. The increase in the relative and absolute importance of DMEK is also in line with previously published data [25,26,27]. Looking at the change in the spectrum of indications leading to surgery, it is surprising that there is a reciprocal development with regard to KC. However, KC is expected to remain the main indication for penetrating keratoplasty. Moreover, PK will remain the gold-standard for therapeutic indications such as corneal ulcers. In other centers similar developments were described [28]. A recent retrospective multicenter analysis clearly shows that eye centers in Germany are now concentrating mainly on posterior lamellar keratoplasty and are primarily performing DMEK as its main representative. In North America and Australia, too, posterior lamellar keratoplasty has been performed predominantly in recent years. It is noticeable, however, that DS(A)EK is the most important method in these regions in the last years with a rising trend for DMEK. This trend was again confirmed in the report of the Eye Bank Association of America for 2023, with more DMEK than DSAEK being performed in the USA in that year for the first time. DALK, as the main representative of anterior lamellar keratoplasty, has been shown to have low but stable numbers over the years, suggesting that DALK retains its relevance for a small range of indications such as moderate keratoconus or anterior corneal scars without Descemet's membrane involvement. This trend is consistent with previously published data [15]. One common feature in all these regions, though, is that PKP is the second most common technology [15, 29,30,31]. Especially corneal ulcers can hardly be compensated by lamellar surgery techniques. With FED being the most important indication quantitatively, the increase of performed DMEK is not yet at its peak, and our data suggest that there will be an ongoing increase in the absolute number of DMEK performed in the coming years. Besides keratoprosthesis the only therapeutic option for existing bilateral limbal stem cell insufficiency, especially in chronic diseases such as ocular pemphigoid, is limbo-keratoplasty. Accordingly, the numbers have remained largely stable over the years, as there is still no established easy alternative, and the long-term results indicate a low graft rejection rate [32].

Comparing the results to other global regions it is striking, that in Northern America the relevance of bullous keratopathy leading to PK is still quantitatively the most important indication. We attribute this to the high quality standard and center-based cataract surgeons as well as the decline of anterior chamber intraocular lenses at our eye center, while in other regions, including the United States, this type of intraocular lens is still prevalent [33].

In the last decade, there was a relative increase of performed penetrating keratoplasties due to KC. This can best be explained by the fact, that the relative proportion of patients with FED leading to PK declined as DMEK is now the gold standard in this case [34].

It is worth noting that the number of PK leading to repeat keratoplasties has increased in recent years, while the proportion of repeat keratoplasties after initially performed DMEK has remained relatively stable. With regard to the shift of patients with FED, who are now usually treated initially with DMEK, it should be borne in mind that the proportion of complicated PKs is increasing and hence the relative number of repeat keratoplasties is rising accordingly.

While the total number of PK performed has decreased over the last two decades, the total number of therapeutic PK has also decreased accordingly. It has also been shown that the relative share of corneal grafts also experienced a negative trend during this period. Nevertheless, it must be emphasized that the proportion has remained relatively stable over the last 10 years. This clearly underlines how important it is for a corneal bank to keep a large variety of corneal buttons in stock, especially for therapeutic indications for performing a PK, as alternative procedures have not yet been established. It is important to note that as certain surgical methods decline in use, it is crucial to maintain the necessary training and surgical expertise to ensure the availability of these techniques when needed.

It must be taken into account that the monocentric design of this study only reveals the trends at LIONS BW cornea bank, Eye Center Freiburg, Nevertheless, similar trends as described above have been identified in other eye centers. It must also be considered that this is only a descriptive retrospective analysis. It is also important to bear in mind that no statement can be made about the indication and surgical technique etc. for transplants sent to external surgeons.

Considering the air-line distance using the postal codes of each patient in the years 2004 to 2010, the distance was constantly rising with a peak of approx. 175 km linear distance. From then on, travel distance slightly declined on a relatively high level of about 100 to 125 km. On the one hand, the data underlines the importance of the eye center for a large area, especially when new techniques such as DMEK are being established.