What does it involve?
The scleral-corneal limbus is a transition zone, a ring surrounding the cornea, in which the cornea and surrounding conjunctiva join. This peripheral zone of the cornea also contains corneal epithelial stem cells, which, after growing in the limbus, migrate over the cornea from the periphery towards the centre, where they are eventually lost by desquamation.
There are a number of congenital or acquired factors that can seriously damage the limbus and, consequently, the stem cell population, causing a condition known as limbal stem cell deficiency syndrome. Limbal stem cell deficiency is caused when there is no longer a limbal stem cell source for corneal epithelial cells. The result is an invasion of conjunctival epithelial cells over the cornea, which take advantage of the fact that the limbus has ceased to act as a barrier to inhibit the growth of the conjunctiva.
The expansion of the conjunctival epithelium over the cornea causes vision loss, as well as epithelial adhesion problems, corneal erosion and ulcers, chronic inflammation and abnormal blood vessel growth. When the limbal stem cell deficiency has not yet fully developed, it can be treated with eye drops. In severe cases, however, limbal stem cell transplantation is the best option.
When is it carried out?
When the limbal stem cell deficiency has not yet fully developed and its cause has been eliminated with the help of medical treatment administered in the form of eye drops, the lesions can recover and stabilise.
In cases where the limbus is severely and extensively damaged in its entirety, there is no possibility of regeneration and medical treatments are ineffective. When this happens, the only effective treatment is surgical and involves transplanting the stem cells again. In recent years, an alternative method has been developed to transplant corneal epithelial stem cells, which consists of removing a small sample of healthy limbus, either from the patient or a donor, cultivating it in the laboratory and subsequently transplanting the stem cells.
A comprehensive eye examination is required to determine the type of conjunctivitis the patient is suffering from.
Before the surgery
In cases of complete limbal stem cell deficiency and corneal opacity, keratoprosthesis (artificial corneas) can also be used. Although surgery is technically easier than limbal transplantation and short-term visual results are very good, the risk of severe medium- and long-term complications is far higher with keratoprosthesis.
The stem cells to be transplanted can be from a donor (allogeneic) or from the healthy eye of the patient (autologous), in which case only a portion of the limbus (a maximum of half) can be extracted.
In cases of complete limbal stem cell deficiency and corneal opacity, isolated corneal transplantation always fails within a few months of surgery, because the absence of corneal epithelial stem cells produces progressive opacification of the transplanted cornea.