Burman and Sangwan Figure 3 Slit lamp photo of total (A) and partial (B) limbal stem cell deﬁciency due to chemical injury. Mechanical debridement can also be used to prevent migration of conjunctival epithelium on to the cornea in acute situations, with partial corneal and limbal epithelial loss. Close observation of patients with thermal, chemical or mechanical epithelial loss involving the limbus, will allow one to detect the advancing conjunctival epithelial sheet and prevent it from extending on to and beyond the limbus (Coster et al 1995). Tseng and colleagues (1998) have successfully used amniotic membrane transplanta- tion (AMT) and mechanical debridement and advocate its use to treat patients with partial stem cell deﬁciency. Their study showed that with partial or focal limbal stem cell deﬁciency, AMT improves both the corneal surface and the vision (Tseng et al 1998). In patients with total limbal stem cell deﬁciency, limbal auto- or allo-transplantation is indicated for corneal surface reconstruction. This may be combined with or followed by 492 keratoplasty. Several modiﬁcations have been described of the technique proposed by Kenyon and Tseng (1989). All these procedures aim to transplant a new source of epithelium for a diseased ocular surface and the removal of the host’s altered corneal epithelium and pannus. After successful transplantation, the host’s cornea (or grafted cornea) will be permanently covered by epithelium from the donor limbus. Although all techniques used in stem cell transplantation are in principle similar, the source of donor stem cells can vary. Donor tissue can be obtained from the fellow eye (lim- bal autograft) in cases of unilateral disease, or from a living related donor (usually gives a better tissue match), or from a cadaver donor (limbal allograft) when both eyes are affected. Limbal transplantation procedures also vary depending on the carrier tissue used for the transfer of the limbal stem cells. Carrier tissue is needed in limbal transplants because it is not possible to transfer limbal stem cells alone. Limbal transplant procedures have used either conjunctiva (conjunctival limbal graft) or cornea (keratolimbal graft) as a carrier tissue for limbal stem cells (Dua et al 2000). Tseng and colleagues (1998) used AMT associated with limbal transplantation in cases with total stem cell deﬁciency. In the past decade some authors have used conjunctival transplantation to treat corneal stem cell deﬁciency. This practice was supported by the belief that conjunctival epithelium “transdifferentiates” into cornea-like epithelium. However, conjunctival epithelial transdifferentiation (that is, acquisition of morphologic, bio- chemical, and physiologic transplantation properties of cor- neal epithelium) does not occur in humans and conjunctival transplantation to reconstruct the corneal surface in stem cell deﬁciency is inferior to limbal transplantation (Tseng et al 1984). Conjunctival transplantation is, however, useful in other conditions, for example, to reconstruct the conjunctival surface in cases of symblepharon and to treat primary and recurrent pterygia. Keratoepithelioplasty was proposed by Thoft as another alternative to reconstruct the ocular surface in patients with conjunctivalisation of the corneal surface (Dua et al 2000). In this technique, lenticules of peripheral corneal epithelium with superﬁcial stroma, were grafted. A few years later the same author modiﬁed the technique to include limbal tissue, acknowledging the importance of stem cell transplantation in these conditions (Dua et al 2000). Successful limbal transplantation can achieve rapid sur- face healing, stable ocular surface without recurrent erosions or persistent epithelial defects, regression of corneal vascu- larisation and restoration of a smooth and optically improved ocular surface, resulting in improved visual acuity and, prob- ably, increased success for subsequent keratoplasty. Clinical Ophthalmology 2008:2(3)