The effect of neonatal monocular enucleation on the optic nerves of the rat.

It is known that removal of one eye in the rat in early postnatal life results in an aberrant ipsilateral projection from the remaining eye. We have estimated the number of optic nerve fibres in 36 days old Black and White Hooded rats that had been unilaterally enucleated at birth. There was no significant difference in the transverse cross-sectional area of the optic nerves of control and enucleated rats. Control animals had an average of about 109,000 myelinated fibres and about 11,000 unmyelinated fibres. The mean minimum diameter of the myelinated fibres was 0.73 microns. The corresponding values in the unilaterally enucleated animals were not significantly different from control animals. These results are discussed in the context of the previously reported increased ipsilateral projection in unilaterally enucleated rats.