Optic neuritis (ON) is defined by the inflammation of the optic nerve causing visual loss, that can be due to multiple etiologies. Making an early and accurate diagnosis is essential to start correct treatment and predict visual outcome. 

We performed a prospective study including patients with acute ON who attended a public hospital in Buenos Aires, Argentina. Patients were examined with high contrast visual acuity (HCVA), low contrast visual acuity (LCVA), Ishihara plates-test, optical coherence tomography (OCT), visual evoked potentials (VEP) and magnetic resonance imaging (MRI). T student, chi-square test and Pearson correlation were performed to analyze the different variables. 

30 optic nerves of 15 patients, 18 ON-eyes and 12 Non ON-eyes (NON-eyes) were included.

12 had unilateral ON and 3 bilateral ON. Mean age, 32,6 years (18-58).

Mean HCVA in ON-eyes was 0,44 vs 0,96 in NON-eyes (p<0.001), mean LCVA 0,67 vs 1,65 (p<0.001) and Ishihara 3,17 vs 8,75 (p<0.05). Although 5 ON-eyes had HCVA of 10/10 (28%), all had abnormal LCVA (Sensitivity 100%).

RNFL was increased in 13/18 (72,2%) ON-eyes and was significantly higher than NON-eyes (p<0.05).  

P100 latency was abnormal in 12/15 ON-eyes (80%) and amplitude in 7/15.

MRI showed T2-signal increase in the optic nerve of 14/18 (77%) ON-eyes (p<0.001) and gadolinium enhancement in 7/18 vs none of the NON-eyes(p=0,01).  

LCVA has a sensitivity of 100% to diagnose optic neuritis.

GCIP thinning and VEPs amplitude decrease are significantly associated with lower visual acuity. RNFL did not show utility to measure ON severity in the acute period.