[The second, mucus-secreting system of the conjunctiva. Ultrastructural findings]

The second mucus-secreting system (type II cells according to our classification) of the conjunctiva is important for moisturization of the ocular surface epithelia. Ultrastructurally, a merocrine and an apocrine type of secretion can be differentiated. The merocrine secretion (epithelial cells containing homogeneous or inhomogeneous osmiophilic granules) appears more or less in all conjunctival areas. The apocrine mode of secretion is only found in the multilayered cylinder epithelium of the fornix conjunctivae. On the whole, the type II cells with inhomogeneous, osmiophilic vesicles are the most common. In the apical area of these cells secretory vesicles either coalesce with the cell membrane or they are completely released to the cell surface. Within the human conjunctiva about 10% of the superficial epithelial cells have secretory functions. Their number slightly increases in the temporal areas of the conjunctiva and in persons under 20 years and over 60 years of age. These results were obtained by electron microscopical investigations of conjunctival biopsies from 48 persons without conjunctival diseases.