Achievements and future problems with component surgery of the cornea.

Penetrating keratoplasty (PKP) has long been the standard procedure for treating corneal opacification. Recent advances in corneal surgery have enabled us to perform component surgery of the cornea, replacing necessary cells and tissue only instead of changing the entire layer of the cornea. Corneal components can be transplanted as lamellar sections of donor cornea or as ex vivo expanded cell sheets with or without biologic carriers. Transplantation of cultivated epithelial sheets expanded from limbal epithelium or oral mucosal epithelium, deep lamellar keratoplasty (DLKP), and deep lamellar endothelial keratoplasty (DLEK) are already in clinical application. These surgical techniques have the advantage of reducing surgical trauma, risk of immunologic rejection, and refractive error. Furthermore, severe ocular surface diseases caused by total limbal stem-cell deficiency including Stevens-Johnson syndrome can be treated by such epithelial sheet transplantation. Although limbal transplantation (LT) has also been applied for such cases, epithelial sheet transplantation has the advantage of covering the corneal surface during surgery, which may reduce postoperative inflammation. However, the success rate of clinical outcome is still not sufficient. We review the surgical technique of component surgery and compare the clinical results including visual acuity, clarity of the cornea, and neovascularization between LT and epithelial sheet transplantation and among PKP, DLKP, and DLEK in our institute. Further refinements in surgical and biologic technology may take the limits of corneal regenerative medicine to new horizons.