Ontogenesis of the cornea and ciliary body : a morphological and molecular study

Doctoral Thesis


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University of Cape Town

The anterior segment of the eye includes the cornea, lens, iris, ciliary body and trabecular meshwork, with each of these elements playing a vital role in the maintenance of vision. The primary objective of this research is to contribute towards the understanding of how specific genes control tissue specification and structural morphogenesis of the developing anterior segment of the eye. Despite its extensive use as a model organIsm, very little is known about the structure and development of the ciliary body in the mouse eye. Using scanning electron microscopy (SEM) the ciliary processes in the adult mouse were shown to form an irregular pattern, crossing over and interweaving, rather than lying parallel to one another, as observed in other mammals. Histological and SEM studies from E14.5 to P7 revealed that the first morphological sign of differentiation in the ciliary body is the appearance of an annular bulge around the optic cup margin; this is then gradually moulded to form discrete ciliary processes. A striking similarity between the developing capillary network and the adult ciliary folds was observed and suggests that the patterning template for the ciliary processes could be the underlying capillary network. Cell proliferation measurements and cell height assessments indicated that one of the first events occurring during the morphogenesis of ciliary processes is a proliferative surge occurring at about PO in the outer ciliary epithelium. It is likely that this surge together with increasing cell heights leads to a bulging of this layer. After a slight delay, the inner ciliary epithelium responds by proliferating and extending inwards towards the lens. Final shaping of the ciliary processes is achieved through cell height reductions in the inner ciliary epithelium. Gene expression analyses revealed dynamic changes in Bmp4 and LEF] expression patterns over the period of ciliary folding, while TgffJ1i4 expression in the ciliary body did not change during morphogenesis. These differences suggest that these genes play different roles in directing the specification and morphogenesis of the ciliary body. The temporal correlation between mitotic and cell height changes during ciliary body morphogenesis suggests that these processes play an integral role in the shaping of ciliary processes.

Includes bibliographical references.