Component surgery of the cornea.

Penetrating keratoplasty (PKP) has long been the standard procedure for treating irreversible opacification of the cornea from various diseases. The success rate of PKP is high compared with those in other organ transplants because of the low incidence of immunologic rejection. However, once rejection does occur, secondary procedures are inevitably less successful. Cases with vascularized corneas are also prone to undergo rejection, and severe disease causing total destruction of limbal tissue is considered a contraindication for surgery. Recent advances in corneal surgery aim at reducing surgical trauma to the host cornea by replacing only necessary cells and tissue. This approach not only reduces the risk of immunologic rejection but may also yield better refractive results. The various transplantable "components" of the cornea include the epithelium, epithelial stem cells, stroma, and endothelium. Cells from these components can be transplanted as lamellar sections of donor cornea or as sheets using biologic carriers and scaffolds. Procedures such as epithelial sheet transplants using amniotic membrane carriers, deep lamellar keratoplasty, and endothelial lamellar keratoplasty are already in clinical practice. Further refinements in technology will certainly take the limits of corneal surgery to new horizons.