limbal

The limbus, or limbal region, is the transition zone between the transparent cornea and the white sclera of the eye. This circular band around the corneal margin contains the limbal stem cell niche and the Palisades of Vogt. It is rich in blood vessels and serves as a barrier that prevents conjunctival epithelium from invading the cornea while providing a reservoir of stem cells for epithelial renewal.

Function: Limbal stem cells continuously replace the corneal epithelium, which normally turns over about every week to two weeks. The limbus also contributes to corneal transparency by maintaining a distinct, relatively avascular surface and by supporting healing after injury. The specialized architecture of the limbus helps regulate cell migration between the conjunctiva and cornea.

Clinical significance: Damage or deficiency of limbal stem cells, known as limbal stem cell deficiency (LSCD), can lead to conjunctivalization of the cornea, corneal vascularization, scarring, and vision loss. LSCD may result from chemical burns, severe inflammation, ocular surface diseases, contact lens overuse, or autoimmune conditions such as ocular cicatricial pemphigoid.

Treatment: Management may involve transplantation of limbal tissue, including limbal stem cell transplantation from autologous or allogeneic sources. Techniques such as cultivated limbal epithelial transplantation (CLET) or simple limbal epithelial transplantation (SLET) distribute stem cells to restore the corneal surface. Immunosuppression is often required for allogeneic procedures.