Alterations in connections of the corpus callosum following convergent and divergent strabismus.

The connectivity of the corpus callosum in visual cortical areas 17 and 18 was studied in normal cats, in cats reared with unilateral convergent or divergent surgically-induced strabismus, and in a Siamese cat. The extents of the callosal cell and terminal zones were determined following multiple injections of horseradish peroxidase and tritiated amino-acids into one hemisphere. Following surgically-induced strabismus, abnormally wide callosal cell zones were seen in both the left and the right hemisphere irrespective of the direction of eye misalignment. Abnormally wide callosal terminal zones were seen in the hemisphere ipsilateral to the deviating eye in cats reared with unilateral convergent and divergent strabismus. Abnormally wide callosal zones were seen in cats which had strabismus induced as late as postnatal day 36. In a Siamese cat with a naturally-occurring convergent strabismus, callosal cells had a different distribution and were fewer in number compared to normal cats or cats with surgically induced strabismus. This implies that the abnormal callosal connectivity of Siamese cats is not a simple result of strabismus.