Diffuse axonal injury (DAI) is the most common form of closed head injury and is responsible for over a third of all head injury deaths. Axons are the primary constituent of the white matter in the brain, and frequently form aligned tracts in the brain. Research has indicated that traumatic axonal injury occurs when these axons experience tensile strains above a critical level. Our laboratory is currently working toward identifying injurious strain levels for axons using the optic nerve stretch model. The optic nerve is an isolated bundle of aligned central nervous system (CNS) axons, thus, dynamic elongation of the optic nerve is an in vivo approximation of the process by which axons are injured in the brain.