Kerala Journal of Ophthalmology

: 2022  |  Volume : 34  |  Issue : 2  |  Page : 186--190

Supranuclear and internuclear ophthalmoplegia - Gaze palsy

Cyril Mathew George, Padmaja Krishnan, Ashwati Sankar 
 Department of Ophthalmology, MES Medical College Hospital, Malappuram, Kerala, India

Correspondence Address:
Dr. Cyril Mathew George
Department of Ophthalmology, MES Medical College, Perinthalmanna, Malappuram, Kerala


Gaze palsy is the loss of binocular control because of lesions of the pathways above the level of the nucleus.[1] To localize the lesion, an understanding of the supranuclear and internuclear pathways is necessary.

How to cite this article:
George CM, Krishnan P, Sankar A. Supranuclear and internuclear ophthalmoplegia - Gaze palsy.Kerala J Ophthalmol 2022;34:186-190

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George CM, Krishnan P, Sankar A. Supranuclear and internuclear ophthalmoplegia - Gaze palsy. Kerala J Ophthalmol [serial online] 2022 [cited 2023 Feb 2 ];34:186-190
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Gaze is described as binocular, synchronous, and symmetrical eye movements in the same or opposite direction, such that the image of the object of interest falls on the fovea of each eye.

There are six systems of ocular movements, namely, the saccades, smooth pursuit, vestibular reflex, optokinetic, fixation, and vergences.

In this portion, we will discuss the horizontal and vertical saccadic eye movements [Table 1] and smooth pursuit movements [Table 2] along with some common lesions in the pathways.{Table 1}{Table 2}

Saccades are fast eye movements to fixate on an object of interest in the field of view when its image is not on the fovea. The impulse for saccades arises in the frontal eye fields.

Pursuits are slow tracking movements to maintain fixation on a moving object, and the impulse arises from the parieto-occipito-temporal cortex, cerebellum, and the superior colliculus.

Vestibular and tonic neck reflex eye movements maintain the alignment of the retinal image with respect to head position or neck position with the help of vestibular part of the ear and proprioceptors of the neck [Table 3].{Table 3}

Horizontal gaze centre

The horizontal gaze centre, situated in the pons, is formed by the parapontine reticular formation (PPRF) and abducens nucleus. The sixth nerve nucleus contains two types of neurons. About 60% of the motor neurons project directly to the ipsilateral lateral rectus muscle as the abducens nerve, whereas the remaining 40% are interneurons that project via the medial longitudinal fasciculus (MLF) to the medial rectus subnucleus of the contralateral third nerve innervating the medial rectus of the opposite side. The PPRF and sixth nerve nucleus are situated very close to each other such that lesions here can only be differentiated by dissociation of saccadic and pursuit eye movements.

Horizontal gaze pathway

The pathway for horizontal gaze is slightly different for saccadic and pursuit eye movements as impulse to the nucleus arises from different parts of the brain. But both these have a common final pathway beyond the abducens nucleus.

The final common pathway from abducens nucleus consists of the following:

Motor neurons to ipsilateral lateral rectus via abducens nerve that causes abduction of the ipsilateral eye.Internuclear neurons via contralateral MLF to medial rectus subnucleus in third nerve nucleus of opposite side that causes adduction of the contralateral eye.[2]

Therefore, both the eyes move towards the side of stimulated abducens nucleus.

[Table 1]: Saccadic movements

Cortex of one side of the brain controls saccadic eye movements to the opposite side [Figure 1]a.{Figure 1}

[Table 2]: Smooth pursuit movements

Cortex of one side of the brain controls pursuit eye movements to same side. Pathway for pursuit eye movement does not relay in PPRF as pursuit eye movements do not need excitatory burst neurons in PPRF that is required to make high velocity saccades [Figure 1]b.

[Table 3]: Vestibulo Ocular system

Stimulation of horizontal semicircular canal results in horizontal ocular rotations away from the side of the canal. This is the basis of vestibular nystagmus in labyrinthine dysfunction.

Horizontal gaze paresis

Features of horizontal gaze paresis depend on the location of the lesion. Lesions in the pons are the most common cause of horizontal gaze paresis. Common etiologies for any gaze paresis (horizontal and vertical) include the following:

InfarctionHemorrhageMultiple sclerosisTumorCentral pontinemyelinolysisWernicke's encephalopathy.

Progressive supranuclear palsy (vertical saccades are affected mainly, later all eye movements are affected as the disease progresses).

Lesion of the PPRF

Loss of all ipsilateral horizontal saccadic eye movements.

Vestibulo ocular reflex and pursuit eye movements are spared as their fibers innervate the abducens nucleus without relay in PPRF [Figure 2]a.{Figure 2}

Lesion of abducens nucleus/6th nerve nucleus

Loss of all ipsilateral voluntary (saccadic and pursuit) and reflex (vestibulo ocular) conjugate eye movements. Infarction of the anterior cerebellar artery can lead to lesion in the PPRF and/or the abducens nucleus [Figure 2]a.

Internuclear ophthalmoplegia (INO)

INO occurs when lesion is in the MLF that connects the abducens nucleus to contralateral third nerve nucleus (hence, the term internuclear). It can be unilateral or bilateral INO.

Unilateral INO

Ipsilateral adduction deficitContralateral dissociated horizontal abduction nystagmus [Figure 2]b.[3]

INO is considered to be only half gaze palsy. Localization of the lesion in MLF (rostral or caudal) can be made by checking for the involvement of convergence. Stimulus from the near reflex system synapses directly to the third nerve nucleus in the rostral midbrain region. Therefore, if

Convergence normal – caudal MLF lesion;Convergence impaired – rostral midbrain lesion.

Usually, there is no strabismus in primary gaze, but in rostral lesion, patient may have exotropia in primary gaze called as wall-eyed monocular INO.

Bilateral INO

Bilateral adduction deficit with simultaneous abduction nystagmus;

Convergence normal or impaired, based on the location of lesion;When there is exotropia of both eyes in primary gaze, it is called as wall-eyed bilateral INO [Figure 2]b.

One and a half syndrome

Lesion of PPRF or sixth nerve nucleus and MLF on same sideIpsilateral horizontal gaze palsy (one) and ipsilateral INO (half)Convergence will be spared as the lesion in MLF is essentially close to the PPRF [Figure 3]a.{Figure 3}

Eight and half syndrome

One and a half syndrome with facial nerve palsy because of ipsilateral involvement of facial fascicular nerve as it wraps around the abducens nucleus in dorsal pons.

Causes – vascular or demyelinating lesions in the dorsal tegmentum of caudal pons.

Half and half syndrome

Lesion of MLF of one side with ipsilateral sixth nerve fascicular involvement (not sixth nerve nucleus).

Therefore, HALF–HALF horizontal gaze palsy because of INO and other HALF because of sixth nerve palsy [Figure 3]b.

Reverse INO/Lutz posterior INO/INO of abduction

Here, there is abduction restriction on attempted gaze to the same side with contralateral adduction nystagmus that is the reverse of INO.

Reflex pathways are intactDescribed with ipsilateral rostral pontine or mesencephalic lesionsCan be unilateral or bilateral.

Vertical gaze centre

The vertical gaze centre is situated in the midbrain (thalamomesencephalic junction), rostral to superior and inferior colliculus, and is formed by

Rostral interstitial nucleus of the MLF (riMLF)Interstitial nucleus of CajalNucleus of posterior commissurePosterior commissure.

Vertical gaze pathway [Table 4]{Table 4}

Vertical gaze also has saccadic as well as pursuit movements with similar cortical control except the fact that initiation occurs in bilateral cortex for vertical gaze of the eye. The pathways from the higher centers project to the riMLF.[4]

Upgaze pathway [Figure 4]a.{Figure 4}

Upgaze paresis

Dorsal midbrain syndrome/Parinaud syndrome

Lesions of the posterior commissure/nucleus of posterior commissure.Pineal region tumors are a common cause.

Other specific causes include infarction of paramedian/top of basilar artery infarction and obstructive hydrocephalus (Sylvian aqueduct syndrome).

Lid retraction (Collier's sign) – damage to inhibitory neurons to eyelid muscles,Light near dissociation (when pretectal involvement is present).Convergence retraction – nystagmoid movement with altered upgaze because of asynchronous convergent saccades.Skew deviation often with higher eye on the side of the lesion.

Downgaze pathway [Figure 4]b and [Table 5].{Table 5}

Downgaze paresis

Unilateral riMLF lesion

Downward saccade is more affected than upward saccade (as third nerve nuclei receive bilateral innervation from riMLF for upgaze, but not for downgaze).

Bilateral riMLF lesion

More common compared to unilateral riMLF lesion as it occurs because of infarction of paramedian arteries at the top of basilar artery (one medial artery supplies both riMLF).

More severe than unilateral lesions.

Downward saccades are affected more than upward saccades, but a complete vertical gaze paralysis also occurs.

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Conflicts of interest

There are no conflicts of interest.


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