Fig. 14. A. Black horseradish peroxidase (HRP) reaction product fills the ciliary body stroma (asterisk) and blackens the intercellular cleft between adjacent pigmented ciliary epithelial cells, as well as the cleft between the apical surfaces of the pigmented and nonpigmented layers. Further diffusion of HRP toward the posterior chamber is blocked by tight junctions between adjacent nonpigmented epithelial cells (arrowheads). Inset. Higher magnification demonstrates the points of fusion (arrows) between membranes of adjacent nonpigmented ciliary epithelial cells that constitute the tight junction. B. Freeze-fracture electron micrograph demonstrates the branching and anastomosing tight junctional strands of a zonula occludens between adjacent nonpigmented ciliary epithelial cells. (From Morrison JC, Van Buskirk EM, Freddo T. Anatomy, microcirculation and ultrastructure of the ciliary body. In: Ritch R, Shields MB, Krupin T (eds). The Glaucomas. St Louis: CV Mosby, 1989.)