Objective
To evaluate directional diffusivities within the optic nerve in a first event of acute optic neuritis to determine whether decreased axial diffusivity (AD) would predict 6-month visual outcome and optic nerve integrity measures.
Design
Cohort study.
Setting
Academic multiple sclerosis center.
Patients
Referred sample of 25 individuals who presented within 31 days after acute visual symptoms consistent with optic neuritis. Visits were scheduled at baseline, 2 weeks, and 1, 3, 6, and 12 months.
Main Outcome Measures
Visual acuity, contrast sensitivity, visual evoked potentials (VEPs), and thickness of the retinal nerve fiber layer (RNFL).
Results
An incomplete 6-month visual recovery was associated with a lower baseline AD (1.50 μm2/ms [95% confidence interval {CI}, 1.36-1.64 μm2/ms for incomplete recovery vs 1.75 μm2/ms [95% CI, 1.67-1.83 μm2/ms] for complete recovery). Odds of complete recovery decreased by 53% (95% CI, 27%-70%) for every 0.1-unit decrease in baseline AD. A lower baseline AD correlated with worse 6-month visual outcomes in visual acuity (r = 0.40, P = .03), contrast sensitivity (r = 0.41, P = .02), VEP amplitude (r = 0.55, P < .01), VEP latency (r = −0.38, P = .04), and RNFL thickness (r = 0.53, P = .02). Radial diffusivity increased between months 1 and 3 to become higher in those with incomplete recovery at 12 months than in those with complete recovery (1.45 μm2/ms [95% CI, 1.31-1.59 μm2/ms] vs 1.19 μm2/ms [95% CI, 1.10-1.28 μm2/ms]).
Conclusions
Decreased AD in acute optic neuritis was associated with a worse 6-month visual outcome and correlated with VEP and RNFL measures of axon and myelin injury. Axial diffusivity may serve as a marker of axon injury in acute white matter injury.