A Closer Look at Corneal Cross-Linking
Treating and Managing LSCD
By William L. Miller, OD, PhD, FAAO
The corneal limbal region, most likely in the Palisades of Vogt, is supplied with an ample complement of stem cells that in normal patients progress onward toward mature corneal cells within the cornea. However, this is not the case in some patients either as a result of a congenital anomaly or secondary damage to these cells from trauma.
The overarching condition is known as limbal stem cell deficiency (LSCD), which results in a generalized conjunctivalization of the cornea. This creates a much looser anatomical framework that manifests itself as neovascularization, epithelial staining and erosion, easier ingress of leukocytes leading to inflammation, and presence of goblet cells.
Congenital cases are largely a result of aniridia and, to a lesser degree, ectodermal dysplasia. Although aniridia is congenital, long-term prognosis is a progressive worsening of the condition with age resulting in LSCD.
Secondary cases may result from chemical trauma to the cornea, thermal corneal damage, Erythema Multiforme (Stevens-Johnson Syndrome), and vernal keratoconjunctivitis. Mustard gas ocular surface injuries with resultant LSCD have also been reported (Baradaran-Rafii et al, 2011; Javadi et al, 2011).
Additional cases of LSCD may also be caused iatrogenically as a result of multiple surgeries or cryotherapies within or around the limbal region. This may include instances secondary to the adjuvant use of mitomycin-C in treating neoplasias and pterygia. Depending on the injury, the LSCD may be complete, involving the entire circumference of the limbus, or partial from limited injuries or iatrogenic causes.
Diagnosis and Treatment
Although signs may mimic other ocular surface diseases, it is the history with the accompanied objective analysis that will lead you to the diagnosis. Biomicroscopy will reveal an epitheliopathy with often a concurrent neovascularization. In aniridia-associated LSCD, the epitheliopathy manifests during the first decade of life with later neovascular involvement in a centripetal pattern. Without treatment, the condition will worsen, creating subepithelial fibrosis and stromal scarring.
Treatment in early cases of LSCD may include options to maintain ocular surface integrity such as tear supplements. Punctal occlusion may also be considered as a means to retain the tear film's residence time on the ocular surface. Other long-term management strategies may include use of scleral GP lenses. They serve to provide an ample reservoir of tears for the ocular surface, which may delay more invasive surgical approaches to treatment in some patients (Schornack, 2011). The Boston Keratoprosthesis artificial cornea has also been advocated after a surgical intervention has been performed to correct the LSCD (Biber et al, 2011).
Surgical strategies may include a partial or penetrating keratoplasty. Alternatively, a complete LSCD treatment may be resolved with an amniotic membrane or limbal stem cell transplant involving cells from the fellow eye, donor, or cadaver. These are all attempts to reconstruct and replace a satisfactory complement of limbal stem cells and to promote re-epithelialization.
Transplantations may involve combined allografts using cornea/limbal and conjunctival/limbal tissues. A report of oral mucosal sheet transplantation for a complete LSCD provides a unique avenue for ocular surface rehabilitation (Satake et al, 2011).
A more targeted strategy is used for partial cases. This may include debridement of the aberrant corneal tissue at the leading edge and moving distally to the limbus. Following debridement, the underlying anterior limiting lamina is polished using a diamond burr. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #191.
Dr. Miller is an associate professor and chair of the Clinical Sciences Department at the University of Houston College of Optometry. He is a member of the American Academy of Optometry and the AOA where he serves on its Journal Review Board. You can reach him at email@example.com
Contact Lens Spectrum, Issue: October 2011