Chromatic visual evoked potentials indicate early dysfunction of color processing in young patients with demyelinating disease

PURPOSE: Chromatic visual evoked potentials (cVEP) primarily reflect the parvocellular visual pathway function, which has been shown to be predominantly affected in demyelinating disease (DD). The purpose of this study was to evaluate cVEP responses and to compare them with other structural and functional findings in young patients with DD. METHODS: Thirty patients (8-28 years of age) with DD with or without a history of optic neuritis (ON) were investigated. Twenty-five eyes had at least one episode of ON (ON-group) and 35 eyes had no clinically evident episode of ON (nON-group). OCT imaging was performed using a high-resolution spectral-domain OCT (SD-OCT), measuring retinal nerve fiber layer (RNFL) thickness. Pattern reversal electroretinography (PERG) and visual evoked potentials (VEP) were recorded according to the ISCEV standard, and chromatic visual evoked potentials (cVEP) were recorded to isoluminant red-green (R-G) and blue-yellow (B-Y) 7 degrees circle stimuli, composed of horizontal sinusoidal gratings with spatial frequency 2 cycles/ degrees , 90% chromatic contrast and onset-offset (300:700 ms) mode of stimulation. Structural and functional measures were analyzed and compared between the groups. RESULTS: Both general (G) and temporal (T) RNFL thicknesses were reduced below normal limits in most of the eyes. However, in the ON-group (G: 77.5 +/- 20.6, T: 51.4 +/- 23.4 microm), the thinning was more significant (p < 0.001) than in the nON-group (G: 95.4 +/- 12.1, T: 70.1 +/- 11.5 microm). PERG N95 was within normal limits in the nON-group, while it was significantly more affected in the ON-group (7.4 +/- 1.0 vs. 5.1 +/- 2.0 muV; p < 0.0001). Similarly, also VEP P100 latency and amplitude showed a greater percentage of abnormality in the ON-group, the latency being longer (117.2 +/- 16.9 vs. 99.4 +/- 4.6 ms; p < 0.0001) and the amplitude lower (9.1 +/- 5.1 vs. 16.4 +/- 7.5 muV; p < 0.0001). The cVEP N-wave amplitude to R-G and B-Y stimuli was reduced below normal limits in both ON- and nON-groups; however, cVEP to B-Y stimulation were slightly more affected in the ON-group (4.0 +/- 3.8 vs. 5.9 +/- 3.3 microm; p = 0.02). A positive correlation between cVEP amplitude and RNFL thickness and between cVEP amplitude and PERG N95 amplitude, as well as a strong negative correlation between cVEP amplitude and P100 latency was observed. CONCLUSIONS: These findings demonstrate that cVEP indicate early abnormality of parvocellular pathway function in eyes with or without a history of optic neuritis and can be used together with other structural and functional parameters to evaluate visual pathway integrity of young patients with DD.