New insights into the surface cells and glands of the conjunctiva and their relevance to the tear film.

BACKGROUND

A number of features of the conjunctiva are highlighted clinically, but there are limited data on the ultrastructure underlying these features. A series of systematic studies have been undertaken to address this, using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

METHODS

Tissue from pigmented rabbits (2 to 2.5 kg) was prepared for electron microscopy, with special attention being paid to the preparation of the palpebral or bulbar conjunctival tissue by stretching it to its fully extended configuration. The fixative (2% glutaraldehyde in 80 mM cacodylate, pH 7.2 to 7.4, 320 to 340 mOsm/kg) has been previously validated in studies on corneal tissue.

RESULTS

Both SEM and TEM reveal the presence of a substantial network of surface pores and underlying ducts associated with the acini of the tarsal accessory gland of Wolfring. These are predominantly found close to the tarsal-orbital boundary of the palpebral conjunctiva. The ductal system is lined with cells containing prominent secretory granules and has features that suggest that it readily collapses if the tissue is not adequately prepared. The same preparative technique also shows the presence of large and open lymphatic vessels in the stroma under the bulbar conjunctiva. Secretory granules and vesicles can also be found associated with the surface ducts and with the surface cells of the palpebral conjunctiva. Studies on the goblet cells located within the conjunctival cell layers also show that the shape of the cells can change substantially with the preparative technique.

CONCLUSIONS

The outcome of these studies indicate that there is still much to be learned concerning the contribution of the accessory lacrimal glands, secreted mucins, the goblet cells, and the lymphatic system to the maintenance of a normal healthy ocular surface.