Infant limbus: an immunohistological study.

All published literature to date has identified the human corneo-scleral limbus as the site within which stem cells of the ocular surface reside. Recently we described a unique anatomical structure at the limbus, termed the Limbal Epithelial Crypt (LEC) that has features of a putative stem cell niche. In this study we examined infant limbus tissue (donor age 4 months) for evidence of LEC and performed immunohistological comparison between infant limbus and adult LEC. No defined LEC were detected in the infant limbus. However, the entire infant limbus has characteristics resembling adult LEC. Both infant limbus and LEC demonstrated negative expression for desmoglein 3. p63 and integrin beta1 expressions were located to the distal region of the infant limbus and to the basal region of the LEC. ABCG2 expression was positive throughout most of the infant limbus as was connexin 43. Infant limbus and in particular the distal region, appeared to house cells that are more "stem-like" in nature. The LEC may be a result of normal physiological developmental in order to protect and maintain stem cells at the ocular surface.

Impression cytology of the ocular surface.

Impression cytology refers to the application of a cellulose acetate filter to the ocular surface to remove the superficial layers of the ocular surface epithelium. These cells can then be subjected to histological, immunohistological, or molecular analysis. Proper technique is essential as the number of cells sampled can vary considerably. Generally two to three layers of cells are removed in one application but deeper cells can be accessed by repeat application over the same site. Applications for impression cytology include diagnosing a wide range of ocular surface disorders, documenting sequential changes in the conjunctival and corneal surface over time, staging conjunctival squamous metaplasia, and monitoring effects of treatment. It is also a useful investigational tool for analysing ocular surface disease with immunostaining and DNA analysis. It is non-invasive, relatively easy to perform, and yields reliable information about the area sampled with minimal discomfort to the patient. Major ophthalmic centres should develop and introduce this technique into routine clinical practice. This is best achieved with a team approach including the ophthalmologist, pathologist, microbiologist, and the immunologist.