AIM: To determine the diagnostic ability of various visual functions in patients with multiple sclerosis (MS) with and without optic neuritis (ON). METHODS: In this cross-sectional study, we assessed and compared refractive error, visual acuity (VA), and contrast sensitivity (CS) between patients with MS and a matched control group of healthy individuals. The MS patients were further categorized into those with ON and those without. RESULTS: A total of 133 eyes from 133 participants were assessed, including 66 individuals diagnosed with MS. The mean ages for the MS group and the healthy control group were 37.5±4.27y and 38.45±4.60y, respectively (P=0.346). Among the 66 patients with MS, 18 had ON. The presence of MS was associated with a decrease in best-corrected visual acuity (BCVA) and spherical component of refractive error (P<0.05), whereas ON did not lead to any further decline in these parameters (P>0.05). MS was linked to decreased CS at spatial frequencies of 6 and 18 cycles per degree (CPD; P<0.05), while ON in MS patients resulted in an additional decrease in CS at 3 CPD (P=0.03). The most significant sensitivity for distinguishing MS patients from healthy individuals as well as MS patients with ON from those without ON was found with cylindrical component [associated criterion (AC) >-0.75 D; 71.21%] and CS at spatial frequency of 6 CPD (AC ≤1.56; 72.22%), respectively. Conversely, the highest specificity for these diagnostic measures was associated with BCVA (AC >0 logMAR; 97.01%) and CS at a spatial frequency of 12 CPD (AC ≤0.60; 93.75%), respectively. CONCLUSION: MS significantly affects refractive error and CS, with ON further reducing CS. Assessing these visual parameters can improve MS monitoring and management.