PurposeTo examine the thiol-disulphide homeostasis during an optic neuritis episode in patients with multiple sclerosis and the relationship between this homeostasis and P100 wave latency.Materials and methodVisual evoked potential reviews of multiple sclerosis patients who presented with an optic neuritis episode were conducted and P100 latencies were measured. Peripheral blood samples were collected from all patients. Native thiol and total thiol concentrations were measured with the automated method that was recently developed. Their amount of disulphide bonds, disulphide/native thiol, disulphide/total thiol and native thiol/total thiol ratios were calculated. The relationship between P100 latency and thiol-disulphide homeostasis was investigated.ResultsA significant positive correlation was determined between the disulphide/native thiol ratio and both mean P100 latency and maximum P100 latency (p=0.021, r=0.136; p=0.030, r=0.177, respectively).DiscussionAs the balance of the plasma dominated by antioxidants moves towards the oxidant side, in other words as a higher rate of thiol is oxidised from the thiol pool, P100 latency is extended. N-acetylcysteine and alpha lipoic acid as well as thiol supplements can improve the thiol-disulphide balance, reinforce antioxidant defence and it can help in slowing down the demyelinating damage.