Optic neuritis is an acute, inflammatory disease of the optic nerve that is usually accompanied by ocular pain, affects more women than men, and may be associated with multiple sclerosis1. A broad range of visual functions are typically affected. The severity of the visual loss varies from a slight visual field deficit to no light perception. Even when acuity returns to normal, as it generally does over the course of weeks or months, visual function frequently remains abnormal2,3. A common complaint of optic neuritis patients is trouble seeing under reduced illumination conditions, such as driving in a tunnel.