Rapid axonal transport in primate optic nerve. Distribution of pressure-induced interruption.

Six primate eyes were studied after four hours of elevated intraocular pressure. Tissue specimens from the region of the lamina cribrosa were examined in cross section by transmission electron microscopy. Interruption in fast orthograde and retrograde axonal transport was identified in individual axons by noting accumulation of membraneous microorganelles, such as mitochondria and microvesicles within axon cylinders. Although organelle accumulation varied from bundle to bundle, involvement of individual axons was diffuse across the extent of a specific axon bundle. This observation contradicts the apparent association of axonal transport block with crosswise-oriented trabecular beams at the level of the lamina cribrosa as seen in tissue specimens examined in longitudinal section. It also fails to support the notion that blocked axonal transport with elevated pressure is produced by kinking of axons at the lamina.