INSTRUCTIONExamine this patient's eyes.SALIENT FEATURES
· Diplopia.· History of multiple sclerosis.· Neurofibroma (causing pontine gliomas).· Drugs (phenytoin, carbamazepine).
· Nystagmus is more prominent in the abducting eye (Harris' sign).* Diverging squint.· Abduction in either eye is normal, whereas adduction is impaired, i.e. there is dissociation of eye movements. On coveringtheabducting eye, the adduction in the other eye is normal
Proceed as follows:
Tell the examiner that you would like to look for other signs of demyelination: optic atrophy, pale discs, pyramidal signs.
This patient has internuclear ophthalmoplegia (lesion) which is probably due to multiple sclerosis (aetiology).
Where is the lesion?
In the medial longitudinal bundle which connects the sixth nerve nucleus on one side to the third nerve nucleus on the opposite sideof the brainstem. The eye will not adduct because the third nerve and, therefore, the medial rectus have been disconnected from thelateral gaze centre and sixth nucleus of the opposite side.
What are the causes?
· Multiple sclerosis.· Vascular disease.· Tumour (pontine glioma).· Inflammatory lesions of the brainstem.· Drugs (phenytoin, carbamazepine).
How would you investigate?
· MRI scan.· Edrophonium (Tensilon) test to exclude myasthenia.
What are the mechanisms to elicit conjugate gaze?
There are four mechanisms for eliciting conjugate gaze in any direction:1. The saccadic system involves voluntary gaze (even when the eyes are shut). Pathways mediating saccadic gaze arise in thefrontal lobe and pass to the pontine gaze centre.2. The pursuit system allows the subject to follow a moving object. Pathways mediating pursuit movements arise in theparieto-occipital lobe and pass to the pontine gaze centre.3. The optokinetic system involves the restoration of gaze despite movements from the outside world, e.g. while a subject is sittingin a railway train and looking out of the window, the eyes move slowly as the train moves, to be followed by rapid correctivemovement back to the initial position of gaze. This is tested with a hand-held drum bearing vertical black and white stripes.Optokinetic nystagmus is often disturbed even before damage to the pursuit system is apparent.4. The vestibulo-ocular system involves correction of gaze for movements of the head. This is achieved by inputs from thelabyrinths and neck proprioreceptors to the brainstem. The patient is asked to fixate to the examiner's face and the head isbriskly rotated by the examiner from side to side or up and down (doll's head manoeuvre). In supranuclear gaze palsy, thesevestibulo-ocular reflex eye move-ments are preserved, despite the absence of both saccadic and pursuit movements. Calorictests are used to demonstrate the vestibulo-ocular reflex.
1. Diplopia is not a feature of defects in conjugate gaze.
2. The centres for saccadic and pursuit movements in the cerebral hemispheres control deviation of the eyes towards theopposite side of the body. These path-ways descend towards the brainstem and cross before they reach the pons.
3. The centres for conjugate vertical gaze lie in the midbrain.
4. The centres for conjugate downward vertical gaze are not well localized, and lesions both in the midbrain and at the level of theforamen magnum can cause defects of voluntary downgaze.
What do you know about 'Fisher's one and a half syndrome'?
It is a syndrome in which horizontal eye movement is absent and the other eye is capable only of abduction - one and a halfmovements are paralysed. The vertical eye movements and the pupils are normal. The cause is a lesion in the pontine regioninvolving the medial longitudinal fasciculus and the parapontine reticular formation on the same side. This results in failure ofconjugate gaze to the same side, impairment of adduction of the eye, and nystagmus on abduction of the other eye.Internuclear ophthalmoplegia was first reported by Bielschowsky (1902) and then subsequently by Lhermitte in 1922. Spiller in 1924described the necropsy findings, implicated the median longitudinal fasciculus and suggested the name 'ophthalmoplegiainternudearis anterior'.