despite its benefits, the loss of endothelial cells that maintain transparency is much higher in DSEK compared to a full-thickness corneal transplant. The reason may be greater tissue manipulation during surgery, the study concluded. During surgery the patient's corneal endothelium is removed and replaced with donor tissue. With DSEK, the donor includes a thin layer of stroma, as well as endothelium, and is commonly 100–150 μm thick. With DMEK, only the endothelium is transplanted. In the immediate postoperative period the donor tissue is held in position with an air bubble placed inside the eye (the anterior chamber). The tissue self-adheres in a short period and the air is adsorbed into the surrounding tissues. Complications include displacement of the donor tissue requiring repositioning ("refloating"). This is more common with DMEK than DSEK. Folds in the donor tissue may reduce the quality of vision, requiring repair. Rejection of the donor tissue may require repeating the procedure. Gradual reduction in endothelial cell density over time can lead to loss of clarity and require repeating the procedure. Patients with endothelial transplants frequently achieve best corrected vision in the 20/30 to 20/40 range, although some reach 20/20. Optical irregularity at the graft/host interface may limit vision below 20/20. Synthetic corneas Boston keratoprosthesis The Boston keratoprosthesis is the most widely used synthetic cornea to date with over 900 procedures performed worldwide in 2008. The Boston KPro was developed at the Massachusetts Eye and Ear Infirmary under the leadership of Claes Dohlman. AlphaCor In cases where there have been several graft failures or the risk for keratoplasty is high, synthetic corneas can substitute successfully for donor corneas. Such a device contains a peripheral skirt and a transparent central region. These two parts are connected on a molecular level by an interpenetrating polymer network, made from poly-2-hydroxyethyl methacrylate (pHEMA). AlphaCor is a U.S. FDA-approved type of synthetic cornea measuring 7.0 mm in diameter and 0.5 mm in thickness. The main advantages of synthetic corneas are that they are biocompatible, and the network between the parts and the device prevents complications that could arise at their interface. The probability of retention in one large study was estimated at 62% at 2 years follow-up. Osteo-Odonto-Keratoprosthesis In a very rare and complex multi-step surgical procedure, employed to help the most disabled patients, a lamina of the person's tooth is grafted into the eye, with an artificial lens installed in the transplanted