The Rodent Model of Nonarteritic Anterior Ischemic Optic Neuropathy (rNAION)

Summary

The following report describes how to replicate the rodent model of nonarteritic anterior ischemic optic neuropathy (rNAION), using the appropriate dye, contact lens and laser parameters. We also reveal the appropriate steps for evaluating the rNAION lesion in vivo.

Abstract

Nonarteritic anterior ischemic optic neuropathy (NAION) is a focal ischemic lesion of the optic nerve that affects 1/700 individuals throughout their lifetime. NAION results in optic nerve edema, selective loss of the retinal ganglion cell neurons (RGCs) and atrophy of the optic nerve. A rodent model of NAION that expresses most NAION features and sequelae has been developed, which is applicable to both rats and mice. This model utilizes a focal laser application of 532 nm wavelength to illuminate a photoactive dye, Rose Bengal (RB), to cause capillary damage and leakage at the targeted anterior optic nerve (the laminar region). After rNAION induction, there is an early optic nerve ischemia, optic nerve edema, and intraneural inflammation, followed by selective RGC and axonal loss. Since the optic nerve is a CNS white matter tract, the rNAION model is applicable to mechanistic studies of selective white matter ischemia, as well as neuroprotective analyses and short and long-term mechanisms of glial and neuronal response to ischemia.

Introduction

Nonarteritic anterior ischemic optic neuropathy (NAION) is a focal ischemic lesion of the anterior portion of the optic nerve (ON)¹. NAION is the most common cause of sudden optic nerve related vision loss in individuals over the age of 50². The mechanism is believed to be a compartment syndrome that results in intraneural edema, and causes compression of the capillaries supplying the axons within the optic nerve³.

Since the ON is actually a central nervous system (CNS) tract, the rodent NAION (rNAION) model can be used to study the mechanisms and responses to isolated CNS white matter strokes. The rNAION mo....

Protocol

This protocol was approved by the University of Maryland Institutional Animal Care and Utilization Committee (IACUC; Baltimore, MD, USA)

1. Experimental Set-up

1. Make a custom designed contact lens from a clear optical grade circular 7 mm in diameter Plexiglas, of 3 mm thickness. Cut the circular lenses with a drill press. Use a standard drill bit to make the inner curve, and finally polish the outer and inner curves using a contact lens polisher of ultrafine grit (1000/3000).
2. Prepare 2.5 mM Rose Bengal (RB) in pH 7.4 phosphate buffer saline (PBS) in advance, filter sterilize with a 0.45 micron syringe filter and store 1....

Results

The contact lens enabled central retina visualization (Figure 1). The focal laser spot illuminates the optic disc at the back of the retina (Figure 2). The normal un-induced retina is shown imaged by slit lamp bio-microscope (Figure 3A) and by SD-OCT (Figure 3B and 3C). During laser induction, when no dye is present in the circulation, laser light does not result in vessel and disk fluorescence (Figure 4A.......

Discussion

While there are a number of models of optic nerve damage (optic nerve crush¹², optic nerve transection¹³, and PION¹⁴), the rNAION model is humane, adaptable to both rats and mice. It more closely resembles the human clinical condition of NAION. This condition includes progressive anterior optic nerve edema, an anterior optic nerve compartment syndrome, focal axonal ischemia, isolated retinal ganglion cell axonal damage and loss over a prolonged time course. The current report gives the ap.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
50 mW 532 nm laser	Iridex		Standard Ophthalmic Laser
0 - 100 mW 532 nm laser	Laserglow technologies		Substitute for iridex
Laser slit lamp adapter	Iridex		SMA coupled adapter for laser output
Coherent Fieldmate laser meter with thermopile sensor	Coherent		others also appropriate
Ophthalmic Examing Slit lamp biomicroscope	Various		Haag-Streit is the best; cheaper versions available on ebay
Rose Bengal	Sigma	330000-1G	Photoinducing agent
Fundus Contact lens or glass cover slip	custom/Cantor and Nissel (UK)		Custom designed planoconvex plastic lens for eye exam and induction
Tropicamide 1%
Tamiya polishing compound	Tamiya, INC	87068	polishing contact lens
2.5% Hypromellose (Goniovisc)/1% Methycellulose	HUB Pharmaceuticals		contact lens coupling agent
2.5% Neosynephrine Ophthalmic drops	Alcon labs		pupil dilating agent
Tropicamide 1%	Alcon labs		pupil dilating agent
0.5% Proparacaine	Alcon labs		topical Anesthetic
30 G fused needle insulin syringe	Various	Various	for intravenous injection of rose bengal
Ophthamic Antibiotic ointment with dexamethasone added (Triple antibiotic ointment)	Various	Various	Apply after induciton to minimize corneal scarring
Heidelberg Corporation Spectral domain-Optical Coherence Tomograph	Heidelberg Corporation		For Optical coherence measurements baseline and post-induction; not essential for induction