cultivated limbal and oral mucosal epithelial transplantation

stem cells located at the limbus ,  are the ultimate source for regeneration of the corneal epithelium in the normal and traumatized states.  when limbal stem cells are dysfunctional or deficient, limbal stem cell deficiency (lscd) develops. its surgical management depends on laterality and severity of corneal-limbal involvement. conventional methods of stem cell transplantation are conjunctival-limbal autograft (clau); conjunctival-limbal allograft (clal) and kerato-limbal allograft (klal) surgeries. cultivated limbal epithelial transplantation (clet) and cultivated oral mucosal epithelial transplantation (comet) on a carrier such as amniotic membrane are current surgical alternatives. these new surgical procedures are effective in stabilizing the ocular surface. the theoretical advantage of ex vivo expansions over conventional methods is that only a small limbal or mucosal biopsy is needed, thus minimizing the risk to the donor eye; and has a lower risk of rejection. they can be used in cases with unilateral or bilateral total stem cell deficiency. in the unilateral cases, the source for clet is healthy fellow eye and in bilateral cases, the source can be living-related or cadaveric eyes.the oral explants do not have limbal stem cells, but they seem to be a source of limbal stem cell equivalents that are able to generate cornea-like epithelium under the proper culture conditions. the main advantage of comet is that patients with bilateral lscd, can be treated with grafts derived from their own autologous oral mucosal cells. the long-term outcomes of comet have to be elucidated.