Summary of Results

The precorneal fluid, which is of great optical importance, forms a film in so far as it can remain almost immobile in the vertical position in spite of the pull of gravity. At slit lamp microscopy corpuscles are seen in the film. These corpuscles are stationary, but may be displaced by the lid margins. The film is displaced as a stable but compressible and elastic structure. This displacement phenomenon has been found to be dependent on the epithelial surface, since it is absent in epithelial defects and certain epithelial disorders. Towards the lid margins the film is delimited by the lachrymal rivus, which extends to the orifices of the Meibomian glands. The lid margins exert a framing effect. If the framing effect is eliminated by pulling the lids away from the bulbus, the film loses its stability and will soon show a spotwise drying up. The film is rather independent of the osmolarity of the conjunctival fluid, but it is sensitive to changes in the hydrogen ion concentration as well as to the presence of certain ions and soaps, which may cause the film to be deranged. In the superficial epithelial cells a lipid layer has been shown histochemically, and this layer mainly consists of phospholipids. There is no suggestion that the lipids are formed in the epithelium, and they are therefore assumed to be rubbed into the epithelial surface. The lipids in the epithelial surface seems to be partly converted into lipofuscins. There are no signs of a keratinization. The superficial cells show a strong activity of acid phosphatase, and the oxidative metabolism takes place even in the outermost cells. By electron microscopy the superficial cells are found to be vital with nuclei and endoplasmatic reticulum. The cytoplasm shows a uniform structure. There are distinct signs of pinocytosis in the superficial cells. The microvilli on the surface known from cats can also be demonstrated in man, and their genesis and function are discussed. After a study of the lid margins, the Meibomian glands, and their secreted lipid emulsion it is assumed that the lipids of the corneal surface originate from the Meibomian glands, being partly rubbed in by the lid margin and partly absorbed by pinocytosis. In a number of histochemical reactions a correlation between the lipids in the epithelium and in the Meibomian glands is demonstrated. A few deviating results can be fully explained. No lipids have been found in the other glands of the conjunctival sac.