Optimization of Crush Force in a Porcine Model of Traumatic Optic Neuropathy

Abstract

Purpose : The purpose of this study is to identify the crush force required to damage the porcine optic nerve sufficient to abolish axonal transport and disrupt electrophysiologic activity.

Methods : Lateral orbitotomies were performed on female Yucatan mini pigs (Sus scrofa domestica). Optic nerves were lesioned by one of 4 methods (N=2 pigs per group): an aneurysm clip applied for 10 s (Standard Crush); an aneurysm clip with force enhancer (Enhanced Crush); a hemostat with cushions over the serrated jaws (Hemostat); lastly, transection of the nerve (Transected). The incisions were closed and animals recovered from anesthesia. Flash visual evoked potential (fVEP) was performed prior to nerve lesion, then 14 days post-operatively. Anterograde axon labeling using intra-vitreal injection of cholera toxin-β subunit (CT-β) was performed 2 days prior to humane euthanasia. Trans-cardiac perfusion fixation, followed by immediate tissue extraction and post-fixation, was performed prior to sectioning and histological analysis.

Results : Significant differences in axonal transport, as measured by CT-β labeling, differentiated the lesions performed on the optic nerve. Additionally, fVEP showed varying degrees of residual electrophysiologic function. Application of the Standard Crush to the optic nerve caused significant depression of fVEP amplitudes, but axonal transport of CT-β was evident beyond the crush site. In comparison, the hemostat lesioned optic nerves showed significant amplitude reductions, as well as CT-β transport up to, but not beyond, the lesion site. Transected optic nerves displayed a relatively flat fVEP and no CT-β transport beyond the lesion site.

Conclusions : Comparison of the effects of the 4 different injury methods suggests that there is a different threshold of nerve damage required to affect nerve electrophysiology; in comparison to that required to affect axonal transport. This information will be necessary prior to evaluating agents that have demonstrated regeneration of the optic nerve in rodents.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.