Experimental: Corneal Crosslinking (CXL)

In the intervention group, the study intervention (CXL) will be administered to stabilize therecipient cornea (which remains in place after penetrating keratoplasty) and to reduce CoNV 8 to 10 weeks prior to corneal transplantation. The study intervention will be repeated once (after 4 weeks prior to transplantation at the latest at the earliest) if insufficient (less than 50%) reduction of CoNV should be observed (to be decided by the respective surgeon). (Protocol V04\_0 Page 45) Corneal transplantation will be performed as standard full-thickness penetrating procedure, and the graft (6.5 to 8.25 in diameter) will be secured with 16-24 interrupted single or 2 double running 10-0 nylon sutures (decision by the surgeon). In case of residual CoNV in the intervention group, visible vessels will may be thermally occluded by fine needle diathermy to avoid intraoperative bleeding and reduce complications (to be decided by the respective surgeon at start of surgery). (Protocol V04\_0 Page 46)

No_intervention: control group

In the control group subjects will be directly scheduled for corneal transplantation without previous CXL. A sham CXL procedure will not be performed. Corneal transplantation will be performed as standard full-thickness penetrating procedure, and the graft (6.5 to 8.25 in diameter) will be secured with 16-24 interrupted single or 2 double running 10-0 nylon sutures (decision by the surgeon). In case of residual CoNV in the intervention group, visible vessels will may be thermally occluded by fine needle diathermy to avoid intraoperative bleeding and reduce complications (to be decided by the respective surgeon at start of surgery). In the control group, no fine needle diathermy will be performed, as this procedure combined with corneal transplantation in previously non-crosslinked eyes might lead to fistulas and thereby to potential intraocular infections. (Protocol V04\_0 Page 46)