Diplopia may result from demyelination affecting the brain stem pathway of the III, IV or VI cranial nerves. Abnormality of eye movements with or without diplopia occurs when supranuclear or internuclear connections are involved. The latter results from a lesion in the medial longitudinal fasciculus - internuclear ophthalmoplegia - and in young persons is pathognomonic of MS.
Nystagmus in abducting eye
Nystagmus may be an incidental finding on neurological examination. Its presence should be sought as evidence of a second lesion. It is unusual in multiple sclerosis when the eyes are in the primary position, and is commonly seen on lateral gaze. Pupillary abnormalities may occur from:
- sympathetic involvement in the brain stem (Horner's syndrome)
- Ill nerve involvement, or
- II nerve involvement.
The swinging light test is a sensitive test of impaired afferent conduction in the II nerve. Alternating the light from one eye to the other results eventually in 'pupillary escape' - the pupil dilates despite the presence of direct light.
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