Long-term neural regeneration in the rabbit following 180 degrees limbal incision.

Penetrating 180 degrees superior limbal incisions were made on the right eye of four adult New Zealand albino rabbits. The contralateral eye served as control. Corneal touch thresholds (CTT) for the central, superior and inferior cornea (2-3 mm from limbus) were determined 3, 9, 15, 24 and 30 months after surgery. In all animals, the CTT was significantly elevated in the superior region of the cornea throughout the measurement period. CTT was elevated in the central and inferior cornea 3 months following surgery and was not affected in the inferior cornea on all other occasions. The animals were then sacrificed and the corneas subjected to histochemical demonstration of acetylcholinesterase corneal nerves. All rabbits showed a reduction in the number of histochemically detectable stromal nerve trunks in the operated region. These stromal nerve trunks showed regenerative changes including abnormally curved course and a subnormal number of axons within a nerve trunk. Epithelial nerve fiber defects included absence or distorted architecture of the basal epithelial plexus and intra-epithelial terminals. These results indicate that although extensive stromal reinnervation had occurred, the extent and quality of stromal nerves was inadequate to restore a normal epithelial plexus and corneal sensitivity.