The effects of binocular and monocular occlusion on the number of optic nerve axons containing degenerative organelles.

In this study chicks were incubated in the dark and then reared for 2 days with either none, one or both eyes occluded. Cross-sections of the optic nerves were examined for profiles of axons containing accumulations of degenerative organelles. There were significantly more organelle-containing axons in the non-occluded and monocularly occluded birds compared with the binocularly occluded birds. There was no significant difference between the non-occluded and monocular group. Furthermore, there was no significant difference between the occluded and non-occluded eyes of monocular birds. We propose that the rise in organelle-containing axons during development reflects a phenomenon involved in the linking of the eyes, and that visual input to a single eye is sufficient to hasten this process.