Normal optic discYou are looking at a normal optic disc. And yet the patient cannot see because the optic nerve is damaged. How would you know? By finding an afferent pupillary defect with the swinging light pupil test.
Optic neuritis is acute visual loss owing to demyelination of the optic nerve. It may be an isolated autoimmune condition or part of multiple sclerosis.
The patient, aged between 10 and 50 years, complains of acute loss of vision and pain around the eye. Visual acuity is usually depressed, but there are no abnormalities in the eye or its surrounding tissues. The swinging flashlight test shows an afferent pupil defect.
Fortunately, vision recovers to normal or near normal in over 90% of patients within six months. No treatment improves those chances.
However, a large collaborative trial conducted in the early 1990s showed that methylprednisolone 1 gm/day for three days, followed by 1 mg/kg oral prednisone for 11 days, significantly reduced the two-year chances of new neurologic events typical of multiple sclerosis. After that time, there was no treatment benefit.
What to do?
Refer urgently all patients suspected of having acute retrobulbar optic neuropathy. If they do not have optic neuritis, they may have other treatable problems such as brain tumor, aneurysm, or infection.