Saturday, December 11, 2010

Corneal Limbus

The corneal limbus is the border of the cornea where it joins the sclera. The human corneal limbus features radially oriented fibrovascular ridges known as the palisades of Vogt which contain pigment granules that are aligned with the microplicae of the epithelium. The limbus is a common site for the occurrence of corneal epithelial neoplasm.

Although it is presumed that the corneal limbus pigment granules are produced by melanocytes, the characterization of melanocytes in the limbus has not been clearly documented. Human limbal tissues has been examined by whole mounts and serial histological sections to localize epithelial cells containing melanin granules. Most of the pigmented cells observed by immunohistochemistry were K19 (+) cells in the basal limbal epithelium.

A superimposed image revealed that melanin granules were oriented towards the apex of each K19 (+) cell, acting as a pigmented cap facing the ocular surface. Melanocytes were identified by MART1, an antigen specific to melanocyte-lineage cells. Melanocytes were shown to exist as sporadic cells with dendritic processes that extend to surrounding epithelial cells.