Horizontal Gaze Palsy

Question 1

Horizontal Gaze centre location + control

Answer 1

The horizontal gaze center is located in the paramedian pontine reticular formation (PPRF) of the brainstem, which is situated in the pons. The PPRF controls the movement of the eyes horizontally, allowing them to move from side to side. The horizontal gaze centre is in the pons at the level of the 6th nerve nucleus
Horizontal movement to the left is controlled by the left horizontal gaze centre, and vice-versa for the right

Question 2

Horizontal Gaze Palsy

Answer 2

A horizontal gaze palsy can result from (1) a lesion involving the sixth nerve nucleus (VI) or (2) a lesion of the pontine paramedian reticular formation (PPRF).

Question 3

Horizontal Gaze Palsy features

Answer 3

Gaze Palsies:
An inability to make a conjugate ocular movement in one direction
This does not cause diplopia since the visual axes remain parallel
By investigating each reflex and conjugate movement in turn, it is possible to establish where a lesion exists
Eye movements affected on ipsilateral gaze but unaffected on contralateral gaze.
Severe damage leads to complete palsy of ipsilateral horizontal gaze.
A PPRF and sixth nerve nucleus lesion can result in similar deficiency of ipsilateral gaze.

Question 4

Horizontal BIL Gaze Palsy

Answer 4

Can arise from bilateral pontine lesions restricted to PPRF or sixth nerve nuclei.
Causes include infarction and tumor.
Selective saccadic palsies or nonselective loss of all horizontal eye movement may result in addition to slowing of vertical saccades.

Question 5

Horizontal Gaze Palsy mx

Answer 5

Mx: Head turns associated with horizontal gaze ­palsies can be managed in a similar way to that described for vertical gaze palsies. Patients with head turns greater than 20° may benefit from surgical intervention using the Kestenbaum procedure normally reserved for the management of nystagmus

Question 6

Horizontal Gaze pathway

Answer 6

Fibres from the gaze centre:
Pass to the ipsilateral sixth nerve nucleus.

Sixth nerve nucleus:
Contains motor neurones that pass axons to ipsilateral lateral rectus muscle (sixth cranial nerve).
Contains interneurons projecting to medial rectus subnucleus of contralateral third nerve via medial longitudinal fasciculus (MLF).

Question 7

Abducens nucleus lesion vs PPRF lesion

Answer 7

Abducens nucleus :
Nonselective ipsilateral horizontal gaze palsy (PPRF = Selective ipsilateral horizontal saccadic gaze palsy)

Abducens= Eyes unable to cross midline (total palsy) + VOR affected (PPRF = Preservation of ipsilateral pursuit and VOR (localised lesions))

Abducens= Saccades made in contralateral hemifield towards affected side are preserved
but slow (PPRF = Saccades made in contralateral hemifield towards affected side are slow and hypometric and may be absent)