Published on December 12, 2007
However, for those whose vision loss is the result of corneal damage from severe infections, chemical burns, Steven Johnson's syndrome or severe drug allergies, the condition can be improved by a new procedure known as Limbal Stem Cell Transplantation.
The cornea is the transparent front part of the eye and is responsible for focusing light rays to the back of the eye. For good visualisation, the cornea must remain transparent and does not have any blood vessels at all.
The white surface area of the eyeball - the sclera - is covered by the conjunctiva and stretches to the corneo-scleral margin called the limbus. This circular area contains stem cells of the corneal epithelium, which regenerate and remain clear. These stem cells are believed to act as a barrier, protecting against the overgrowth of the conjunctiva, which is enriched by tiny blood vessels.
According to ophthalmologist Dr Pinnita Tanthuwanit, most corneal abrasions or ulcers arising from minor injuries heal nicely without scarring. But severe chemical burns or Steven Johnson's syndrome may cause persistent non-healing corneal epithelial defects because the corneal stem cells fail to produce sufficient epithelial cells. This condition is called limbal stem cell deficiency and leaves the eye vulnerable to infection, leading to scarring and/or perforation. Eventually, non corneal cells from the conjunctiva overgrow, covering the cornea and cause it to lose its transparency.
Treating such conditions with a simple corneal transplantation or penetrating keratoplasty surgery will not succeed because a corneal transplant replaces only the central cornea and not the limbus where the stem cell of the corneal epithelium resides. However, limbal stem cell transplantation with or without subsequent corneal transplant is helpful and is now being offered at Siriraj Hospital.
If the corneal scar is localised or partially affected, only scar tissue containing blood vessels will be removed and a partial transplant of limbal stem cells taken from the other good eye will be performed. In patients with entire corneal scarring in one eye, a more autologous, limbal stem cell transplant is performed over a six-hour period.
Allografts can also be performed if both eyes are affected, meaning the limbal stem cells are taken from donors, either living (usually related) or cadaveric. That, however, requires systemic immunosuppression with medicines.
Both autogenous and allogenous grafts have been undertaken at Siriraj since 1997. But both procedures have suffered problems with a high rate of rejection in allotransplants and inadequate stem cells harvested for autogenous surgery.
Dr Pinnita and his team are now cultivating removed stem cells and growing them in appropriate media prior to transplantation, a techniques pioneered by Italian doctor Dr Pellegrini and which yields a success rate of up to 75 per cent.
Cultivated corneal epithelial stem cells have been successfully transplanted to three patients suffering from corneal scarring and the preliminary results are promising.
Dr Pinnita concludes that this new technique is feasible thanks to the excellent collaboration between Bangkok Biomaterial Centre, Immunology, Pathology and Ophthalmology. The concept of cultivating limbal stem cells for transplantation, he adds, is exciting and offers new hope to many visually patients.
By supakorn rojanin, md
Chairman, Department of Surgery
Faculty of Medicine Siriraj Hospital,