METHODS: A cross-sectional study was conducted at the Eye Clinic of Hospital Universiti Sains Malaysia(HUSM)between September 2011 and February 2013. We recruited twenty optic neuritis patients with a single episode of idiopathic optic neuritis occurring between 3mo and 2y prior to examination, and twenty control subjects. Ocular examination included visual acuity, colour vision, contrast sensitivity, visual field and pattern VEP. Independent t-test was conducted to compare the differences in the means of optic nerve function and VEP parameters between the optic neuritis group and control group. In parameters that were not normally distributed, Mann-Whitney test was used to compare the medians between the two groups.

RESULTS: In the optic neuritis group, the mean age was 30.8y. The mean duration between the episode of optic neuritis and the time of evaluation was 6.6mo. The visual acuity was poorer in the group with optic neuritis, with the mean LogMAR score(0.52)being significantly higher in this group than in controls(P=0.001). Colour vision was likewise decreased, with a mean score of 63.0% in the optic neuritis group(P=0.001). Contrast sensitivity was reduced in all four spatial frequencies; 3CPD(P=0.029), 6CPD(P=0.026), 12CPD(P=0.002)and 18CPD(P=0.006)in patients with optic neuritis. There was also a statistically significant loss of visual field in this group(P≤0.001). Although subjects with optic neuritis had a slightly prolonged VEP P100 latency compared to normal subjects, this difference in VEP latency was not significant using checkerboard pattern 1 or 2. Higher VEP amplitude was observed in optic neuritis subjects, but the difference between groups was not statistically significant.

CONCLUSION: There were significant reductions in optic nerve functions(i.e. visual acuity, colour vision, contrast sensitivity and visual field)at a mean of 6mo after an acute attack of optic neuritis. However, no significant differences in VEP amplitude and latency were noted between patients with optic neuritis and the control group. VEP may not be the ideal test to diagnose a previous attack of optic neuritis, as VEP parameters tend to normalize after a variable interval.