Evaluation Of The Visual Function In The Rodent Model Of Non-arteritic Ischemic Optic Neuropathy (rnaion)

Abstract

Purpose: : Non-arteritic ischemic optic neuropathy (NAION) is caused by a sudden blood insufficiency for the optic nerve and is a major cause of the optic nerve dysfunction. There is no effective treatment in the present time. Our purpose is to make a rodent model NAION (rNAION) and to evaluate the visual function using the visual evoked potential (VEP) and the electroretinogram (ERG).

Methods: : To induce rNAION, Rose Bengal (RB) (2.5mM) was injected in the tail vein and was photoactivated in the vessels of the optic nerve using 514nm argon green laser with a 514µm spot size for 12 seconds. For the VEP recording, rats were anesthetized with ketaramine/xylazine(100mg/kg and 10mg/kg). Stainless steel screws were implanted at the 6 mm behind the Bregma suture and 3 mm to the midline bilaterally. A reference electrode was placed on the midline of 1 mm in front of the Bregma suture. For VEP recording, Bright flash stimuli (10 ms single full-field flash stimulus with flash intensity of 105 cd/m², 0.03s,3Hz) were given by a contact LED stimulator (WLS-20) produced by Mayo Co. VEP response was averaged for 50 similar stimuli. All rats were dark adapted for over 3 hours prior to the beginning of ERG testing. Retinal signals for ERG were recorded from the cornea using the same contact LED stimulator. The reference needle electrode was placed in the oral cavity. In the stimulation paradigm, series of flashes (20000cd/m², 50 ms duration) were delivered from the back of the animal to avoid any direct illumination of the eyes. VEP and ERG were compared between control and experimental eyes in the same individual.

Results: : VEP responses from individual rNAION rats were significantly reduced, compared with the control eyes. VEP amplitude was decreased and the latency was delayed at the first day after rNAION induction. However, ERG does not show any significant differences between control and experimental eyes.

Conclusions: : The rNAION could be an ideal model and we could do a detailed analysis of the retinal and optic nerve changes that occur after the optic nerve stroke. VEP could be useful for the evaluation of visual function and effectiveness of the various therapeutic options.

Keywords: optic nerve • electrophysiology: non-clinical • ischemia