Corneas for penetrating keratoplasty that have been excised from the globe for storage ordinarily require punching of the donor tissue from the posterior surface. They may be trephined from the anterior surface when they are mounted on an instrument that forms a seal around the scleral rim of the excised cornea, allowing the endothelium to be supported physically by the liquid storage medium. The artificial anterior chamber protected the endothelial cells from damage as if they were still in the intact globe. The instrument allowed trephination to any desired depth and facilitated the cutting of corneal buttons with a rim of Descemet's membrane and endothelium. Sutures may be preplaced in the donor button before the button is seperated completely from the rest of the cornea. Iris prolapse did not interfere with the procedure.