Optic Nerve Crush (ONC)

Summary: Crushing the optic nerve with mechanical damage leads to axon degeneration, in turn inducing the apoptotic process in RGCs and, eventually, RGC loss, mimicking glaucomatous neuropathies.

Optic nerve is composed of retinal ganglion cell (RGC) axons and supporting cells. Some neurodegenerative diseases of the eye, e.g. glaucomatous neuropathies, primarily affect optic nerve. This pathology can be mimicked by damaging the optic nerve. 

In this model, we crush the optic nerve with self-closing forceps. Axons of optic nerve start to degenerate due to mechanical damage. This, in turn, induces the apoptotic process in the RGCs and, eventually, RGC loss. 

The model is acute with a typical follow-up time of 1-2 weeks, but minimally invasive. The induction is unilateral leaving the contralateral eye as naïve control. Currently, topically administered brimonidine tartrate (0.2%) is used as a reference compound to assess RGC function. 

Animal species	Mice, Rats
Method of induction	Subretinal injection
Follow-up period	Up to 7 days
Route of compound administration	Topical (e.g. eye drops), subretinal, intravitreal, systemic
Read-outs	1. In vivo imaging: – Fundoscopy, – Fluorescein angiography, – Optical coherence tomography (OCT), 2. In vivo functional assessment, 3. Morphological assessment, 4. Molecular biology (ELISA, Western blotting, qPCR).

Outcomes and Read-Outs 

In vivo imaging

Doppler imaging (Envisu R2210 and Envisu R2210, Bioptigen Inc./Leica Microsystems) immediately after the induction to verify the blood circulation gets normal within the first 2-3 min. after the crush. This is important to ensure the mechanical damage of the optic nerve is not accompanied by prolonged ischemia. 

SD-OCT retinal thickness imaging. A thinning of the inner retina can be monitored at different timepoints after the crush induction (Maciulaitiene et al., ARVO 2017). The thinning of the inner retina varies from 5% at day 7 post-ONC to 25% at day 28 post-ONC. 

Functional assessment

Pattern electroretinography (pERG) to assess retinal ganglion cell function (Leinonen et al., ARVO 2016). The decrease in the pERG amplitude varies from approx. 30% to 60% depending on the animal species, strain, age and timepoint after the crush. 

Visual evoked potential (VEP) recordings from primary visual cortex. The VEP response is almost undetectable in vehicle-treated ONC eyes at 14 days post-ONC (Leinonen et al., 2016). 

Histology/morphometry

Loss of RGCs and grading of optic nerve damage. There is approx. a 50% loss of RGCs within the first week, and about 90% of RGC loss within a 2-week period after the crush.