Positional specificity of corneal nerves during development.

The developing avian cornea is enclosed within a nerve ring from which numerous neurites extend into the cornea as radially ingrowing, regularly bifurcating fascicles. The authors now assess the degree of positional specificity of developing corneal nerves by photographic comparison and digital computer signal averaging. Such analyses demonstrate that nerves display extensive homology of position within the developing nerve ring, indicating that their growth cones originally followed specific pathways around the cornea. During their extension within the cornea, nerve fascicles bifurcate only within distinct, successive, and concentric zones suggesting that the position of an intra-corneal nerve branch point is designated by the intra-corneal milieu. Since the distance between the branch zones reported here increases with corresponding corneal growth, neurite elongation may occur both at the growth cone and along the axon at inter-branch sites of extending corneal nerves.