Functional and Structural Evaluation of Afferent Visual System in Multiple Sclerosis Patients / Funkcionālas un Strukturālas Redzes Sistēmas Izmaiņas Multiplās Sklerozes Pacientiem

There is insufficient information about the progress and variability of multiple sclerosis (MS). Afferent visual pathways are an appropriate MS clinical model. Optical coherence tomography (OCT) allows to perform precise measurements of axonal tissue in the retinal nerve fibre layer (RNFL). Visual evoked potentials (VEP) provide information about the functional status of visual pathways. The aim of our study was to use OCT and VEP to evaluate MS patients with and without optic neuritis (ON) history and to determine relationships between functional and structural changes. The cross-sectional study included 76 relapsing-remitting MS patients and 28 healthy controls. The lowest mean VEP N75/P100 amplitude was found in ON affected eyes (8.16 mkV, SD = 4.60). However, it was observed that the mean amplitude in patients without ON (M = 9.86; SD = 4.63) was by 4.64 mkV lower than in controls (p < 0.001). Similarly, the mean P 100 latency in ON eyes was 9.26 ms longer than in eyes of patients without ON history (p < 0.01). RNFL in the temporal segment (RNFLT) was the thinnest in ON eyes, and even in patient eyes without ON, it was thinner than in controls. We found a significant positive correlation between RNFLT and mean N75/P100 amplitude in patients without ON (r_s = 0.43; p < 0.001), and after ON (r_s = 0.45; p < 0.001). Both in patients without ON (r_s = -0.40; p < 0.001) and in ON eyes we found a significant negative correlation (r_s = -0.55; p > 0.001) between RNFLT and mean P100 latency. In summary, we found that deterioration in the visual system was not associated with the clinical ON episode. Regardless of ON symptoms in history, there exists correlation between functional and structural changes.