Application of Electric Fields with Asymmetric Charge Balanced Waveforms Directs Optic Nerve Regeneration After Crush Injury

Abstract

Purpose :
There are currently no effective treatments to restore vision in patients blinded by advanced optic neuropathies. Despite significant interest exists in harnessing electric field (EF) application into technology to direct retinal ganglion cell (RGC) axon regeneration, its clnical translation has been limited by dependence on direct current (DCEF) which can lead to charge accumulation and tissue damage. Our group has designed and tested the efficacy of a class of charge-balanced biphasic waveforms to direct and support RGC axon regeneration after crush injury in adult rats.

Methods : Adult male Long-Evans rats were subject to optic nerve crush followed by implantation of an intra-orbital and intracranial electrode. After one week, various charge balanced biphasic waveforms were applied for 5 hours daily for 30 days. These waveforms were either symmetric (SCB) or asymmetric and charge-balanced (ACB). The two groups receiving ACB waveform treatment had a longer pulse width in either the anodic (ACB 1:4) or cathodic phase (ACB 4:1). One week before euthanasia, the animals were injected intravitreally with cholera toxin B (CTB) for anterograde labeling of regenerated axons. Regenerative responses were assessed via histologic, electrophysiologic, behavioral, and pupillary light reflex testing.

Results : Compared to untreated animals (N=5), we observed comparable axon-regeneration at 1000 um past the crush site after treatment with ACB 4:1 (N=4), vs 5-fold more with SCB waveforms (N=2), and 26-fold with ACB 1:4 waveforms (N=5). Local field potential recordings demonstrated greatest partial recovery of visual function in the superior colliculus of ACB 1:4 treated animals, with 19.2% of sites responding (N=8), followed by 5.3% in ACB 4:1 treated animals (N=8), 10.3% with SCB waveform (N=5), and 1.3% in untreated animals (N=5) (ACB 1:4 vs untreated; p ≤ 0.001). On pupillary light reflex testing, each ACB 1:4 treated animal showed consistent pupillary constriction to light (N=10) whereas only 33.3% in the untreated (N=6) and ACB 4:1 (N=6) groups did.

Conclusions : These results suggest that treatment with asymmetric charge-balanced EFs with longer pulse widths in the anodic phase are more effective in promoting RGC survival and directing axon growth with partial recovery of visual function in rats after optic nerve crush than untreated animals or other waveforms.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.