Traditional fundoscopy and structural studies using optical coherence tomography (OCT) suggest that youth with MS have an injury to the temporal quadrant of the retinal nerve fibre layer (RNFL). However, full-field evoked responses may not adequately capture focal injury in different quadrants of the retina, hence missing important information about distinctive disease processes associated with different forms of acquired demyelinating syndromes (ADS). The utility of hemifield evoked responses in the evaluation of youth with ADS/MS is unknown.
To evaluate amplitude and latency differences in evoked responses between youth with ADS, MS and healthy control (HC) using hemifield assessments.
This cross-sectional study included youth with ADS (n=22, MS=11, and Myelin Oligodendrocyte Glycoprotein antibody-related disorders (MOG)=11) and 21 age/sex-matched HC. Evaluations were performed at a minimum of 6 months after a known episode of optic neuritis (ON). Binocular evoked responses to a reversing checkerboard stimulus in each hemifield (nasal and temporal) were recorded in a whole-head 151 channel CTF magnetoencephalography system (VSM MedTech, Vancouver, CA) following a standardized protocol. 1,2,3 Amplitude and latency were then identified using source reconstructed visual evoked responses (MATLAB 8.0, The MathWorks and BrainWave v 3.2)4,5,6. Binomial regression was performed with hemifield as an interaction term to predict disease classification. GEE was used to account for multiple observations in each patient. The analysis was completed using R 4.0.
When assessed separately by hemifield (nasal and temporal), latency did not distinguish HC from ADS or HC from MS. Decreases in amplitude (0.99±1.00nAm) measures overall corresponded to increased probability of MS. This relationship was stronger when measured in the temporal hemifield (X2=0.98). Effect size was small, but statistically significant (p=0.023).
In the chronic state, using visual evoked fields (VEF), the amplitude is more likely than latency to distinguish youth with MS from HC. This effect is accentuated in the temporal hemifield. This reinforces the knowledge that focal axonal injury may occur early on in youth with MS. While significant, the effect size of this relationship was small, suggesting that VEF temporal hemifield amplitude alone may not be adequate to distinguish MS from HC. Future studies should concentrate on the contribution of other morphological features of the VEF waveform to distinguishing MS from other populations.