Abstract
Purpose :
The rodent Nonarteritic Anterior Ischemic Optic Neuropathy (rNAION) model is valuable for understanding the pathophysiology of NAION. Quantitative visual function analysis is important to assess treatment efficacies aimed at neuroregeneration. Flash visual evoked potential (fVEP) is widely used but has large variability across measurements and is extremely sensitive to experimental conditions. Skull screw electrodes increase the signal-to-noise ratio and achieve high reproducibility (You, 2011), but are limited by significant differences in the fVEP waveforms at the visual cortex between flashes in the contralateral versus ipsilateral eye (Montero, 1973). We evaluated repeatability of fVEP using bilateral screw electrodes over the visual cortex, and compared this to data obtained from subdermal needle electrodes.
Methods :
Male Long-Evans rats (~ 250 g) were rNAION induced as previously described (Bernstein, 2003). Three weeks post-induction, rats were dark adapted for >4 hours and anesthetized with ketamine/xylazine. fVEP measurements were done using the Celeris amplifier (Diagnosys LLC) using a subcutaneous needle electrode over the visual cortex. Three days after fVEP, animals were re-anesthetized and two stainless steel screw electrodes were implanted via craniotomy. One week post-surgery, rats were dark adapted, anesthetized, and fVEP was performed using implanted electrodes. Relative visual function of the right eye, as a percentage of the left eye, was calculated from fVEP measurements. Intrasession and intersession coefficients of variation (CV) and intrasession repeatability (r95) were calculated for both types of electrodes.
Results :
Relative visual function calculated from screw fVEP showed intrasession CV of 5.7% ± 3.2%, intersession CV of 9.5% ± 6.7%, and r95 of 21.1% ± 1.5%, while needle fVEP showed intrasession CV of 26.3% ± 19.9% (p < 0.05), intersession CV of 45.0% ± 35.4% (p < 0.05), and r95 of 67.6% ± 12.8% (p < 0.05).
Conclusions :
Despite inherent variability of fVEP, calculation of relative visual function between the two eyes using bilateral skull screw electrodes shows significantly decreased intrasession and intersession variations compared to subcutaneous needle electrodes. This approach greatly increases consistency and decreases the number of animals needed to achieve statistical significance when performing electrophysiological analysis of visual function.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.