Optic Neuritis: General

Optic neuritis, inflammation or demyelination of the optic nerve, is the initial presentation of 15% of patients with MS.

Approximately 50% of all patients who present with optic neuritis have MS. Isolated episodes of optic neuritis, however, even if they are recurrent, are not diagnostic of MS [6].

Eye involvement in MS:

1. Optic Neuritis (ON) is the Inflammation of optic nerve at any point and is a frequent presenting symptom manifesting as:
   • variable degree of visual loss affecting mainly central vision and sometimes decreased colour vision.
   • Relative Afferent Pupillary Defect (RAPD), causing Marcus Gunn Pupil.
   • Fundoscopy may be normal or rarely shows papillitis.
   • Central or cecocentral scotoma on visual field mapping.
   • visual loss is often preceded by retrobulbar or extraocular muscle pain that may be reproduced by periorbital palpation.
   • 90% of patients regain normal vision, typically over a period of 2 to 6 months.
2. Bilateral, simultaneous ON is rare in MS and may suggest other diagnosis.
3. Oculomotor pathway involvement (may be in association with brainstem or vestibulo-ocular lesions):
   • Cranial nerve VI, III and IV may be involved.
   • Nystagmus is common in MS
   • Acquired pendular nystagmus of eyes in primary position is characteristic of MS.
   • Oscillopsia: Subjective oscillation of objects in the field of vision due to nystagmus (often bilateral) is a frequent symptom in MS.

Optic neuritis may also cause an afferent pupil defect or Marcus Gunn pupil. Light directed into one eye should, through the direct light reflex, cause both pupils to contract. If one optic nerve is poorly conducting, swinging light into that eye will result in less transmission and the pupils will now dilate. Swinging light to the normal eye will increase conduction and the pupils will now constrict.