Sukanya Arunachalam1, Yuyi You1,2, Stuart Graham1,2, Adriana Fontes3, Con Yiannikas3, Alexander Klistorner1,2

Purpose: To assess differential patterns of axonal damage and demyelination, measured by multifocal visual evoked potential (mfVEP), in the visual system in neuromyelitis optica (NMO) and multiple sclerosis (MS) patients with optic neuritis (ON).

Methods: NMO (n=9) and MS (n=15) patients and age- and sex- matched healthy controls (n=13) were enrolled in this cross-sectional study. All the patients had a history of clinical ON, but none of them had an acute ON episode within 6 months of this study. All the participants underwent ocular examination, mfVEP recording, Spectralis optical coherence tomography (OCT) scans and Humphrey automated perimetry. The correlation between mfVEP latency delay and amplitude reduction among the three groups were investigated.

Results: A significant latency delay was observed in both NMO (166.76±4.79 ms; p =0.001 vs controls) and MS (169.51±4.79 ms; p<0.001 vs controls) patients compared to the controls (144.49±1.70 ms). However there was no significant difference between the two disease groups (p=0.72). Further, there was an amplitude reduction observed in both patient groups. The amplitude reduction in NMO patients was significantly greater than that in MS patients (86.56±20.75 µV Vs 133.04±15.07 µV; p <0.0001). Conclusion: On comparing the parameters patients with NMO have significant reduction in VEP amplitude compared to the other groups. This decrease in amplitude is thought to correspond to the profound axonal loss seen in the ON eyes of NMO patients. The degree of demyelination is similar in both the disease groups as evidenced by the comparable VEP latency delay measurements.