ABSTRACT
Similar to the central nervous system, a bidirectional axonal flow can be demonstrated in optic nerve axons. An anterograde transport system carries material from the cell body to the axonal terminal, and a retrograde transport system carries material in the opposite direction.The anterograde axonal flow has one fast and one slow component.The materials that are rapidly transported are those involved in synaptic function, while highmolecular-weight proteins and particulate substances that participate in structural maintenance and axonal growth are transported slowly.The velocity of retrograde axonal transport is variable, but it is generally slower than that of the fast component of the anterograde transport. The material that is transported through this system is similar to that transported by the anterograde system. In addition, the retrograde system transports proteins and small molecules that have been picked up at the axonal terminals. Axoplasmic flow is typically altered in glaucoma, leading to accumulation of cellular organelles at the level of the lamina cribrosa.63,64 Ultrastructural alterations in axons exposed to high intraocular pressure seem also to be most marked at the level of the lamina cribrosa sclerae,65 but axonal alterations can even be seen in the optic chiasm.66
