Structural differences between regions of the ciliary body in primates.

The ciliary bodies from four rhesus monkey and six human eyes were subdivided into eight adjacent zones. The morphology of the ciliary epithelium and bordering stroma at the crests of the processes was examined electron microscopically in each region. In two of the monkey eyes (3 months and 18 years old) and in two of the human eyes (18 years and 55 years old) profiles of mitochondria, rough endoplasmic reticulum (RER) and Golgi complexes were counted at different locations, and the values for different zones within each individual eye compared by a multifactoral analysis of variance. Fenestrations in the endothelium of the capillaries in the stroma bordering the epithelium were also counted. The basal and lateral infoldings of the nonpigmented epithelium (NPE) and pigmented epithelium (PE) are most prominent in the anterior and middle areas of the pars plicata (zones I and II). Mitochondria and RER are significantly more frequent in this area. The stromal layer is very thin, and the capillary endothelia exhibit a large number of fenestrations. These findings suggest that the anterior portion of the pars plicata is involved in aqueous humor production. In the transition zones between the pars plicata and pars plana and in the pars plana (zones III to V) the number of mitochondria and RER profiles is decreased. In contrast, Golgi complexes are most frequent in zone IV, perhaps relating to the increased mucopolysaccharide production observed in this area. Special interconnections (wedgelike, mushroomlike, and fingerlike) were observed between the epithelial cells and between the PE and the stroma in zones III to V. These structures may serve as additional mechanical interconnections, which strengthen the tissue and thereby play an important role when it is put under tension during accommodation.