Structural alterations in the ciliary process and the blood-aqueous barrier of the monkey after systemic urea injections.

The structural alterations induced in the monkey ciliary epithelium by intravascular injection of urea solutions were studied with the light and electron microscopes. Arterial injection of urea resulted in destruction of the nonpigmented epithelium and the consequent breakdown of the blood-aqueous barrier. The intravenous injection did not significantly affect the structural integrity of the ciliary epithelium. The intercellular zonulae occludens were not altered and the intercellular pathway from blood to posterior chamber remained closed to horseradish peroxidase. Intercellular uptake in large cytoplasmic vacuoles appeared to account for some late transport to the basal end of the nonpigmented epithelium. There was no comparable transport of peroxidase in vesicles or vacuoles through the nonpigmented epithelium in animals not subjected to intravenous urea treatment. Compared to the arterial route, intravenous administration of urea does not appear to pose a serious threat to the integrity of the ciliary epithelium.