Timing matters when using paraclinical tests to assess for optic neuritis under the 2024 McDonald criteria

The 2024 revisions to the McDonald criteria for multiple sclerosis (MS) add the optic nerve as a fifth central nervous system location—alongside periventricular, juxtacortical/cortical, infratentorial and spinal cord—for demonstrating dissemination in space (DIS) in MS. 1 This change appropriately recognises how often the anterior visual pathways are involved in MS, and codifies the role of paraclinical tests in documenting optic nerve injury. MRI, visual evoked potentials (VEPs) and optical coherence tomography (OCT) assist with this. Below, we discuss the practical implications for clinicians with particular attention to timing of the studies.