The author reviews the differentiating signs, causes, and management of horizontal gaze palsies. These are disorders in which the supranuclear control of lateral eye movements is impaired. Sometimes the palsy is selective for some types of eye movements, but not others (eg, selective saccadic palsy). When acquired, horizontal gaze palsy usually points to damage to specific pontine structures. Congenital forms occur too, such as the Mobius syndrome and horizontal gaze palsy associated with pendular nystagmus and scoliosis. The genetic defect for the latter has been described, and it involves a protein that likely plays a role in axonal guidance during development.
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• Horizontal gaze palsy is usually due to lesions of supranuclear, nuclear, and infranuclear pathways of horizontal of eye movements in the pons.
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• Palsy of all types of horizontal movements implicates the abducens nucleus, whereas palsies of saccades alone are due to lesions of the parapontine reticular formation.
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• Congenital syndromes with horizontal gaze palsies include Mobius syndrome, Cogan congenital ocular motor apraxia, and horizontal gaze palsy with progressive scoliosis.
Historical note and terminology
Gaze palsy is an ambiguous term. It is best restricted for deficits in conjugate eye movements that affect both eyes. Thus, strictly unilateral problems such as palsies of cranial nerves III, IV, or VI are not gaze palsies, even though they do affect gaze. Likewise, impairments in vergence control, such as convergence or divergence insufficiency, are not gaze palsies, as they do not involve conjugate eye movements. In fact, vergence is often spared in horizontal gaze palsies, with some patients using a near reflex as a compensatory maneuver to get at least the adducting eye to move (69).
Gaze palsy also implies that the deficit is limited to some directions of conjugate movements only. Diffuse reduction of all eye movements is best termed ophthalmoparesis. These are most commonly myopathic in origin, occurring with mitochondrial disorders (chronic progressive external ophthalmoplegia, Kearns-Sayre syndrome, MELAS), myotonic dystrophy, oculopharyngeal dystrophy, thyroid eye disease, myasthenia gravis, and congenital fibrosis, among others.
The term “gaze palsy” requires further elaboration. There are many different types of conjugate eye movements, including saccades, pursuit, optokinetic, and vestibulo-ocular responses. The anatomic systems that control these diverge and converge at various levels, and it is possible for some lesions to impair some eye movement systems and spare others. Hence, a left saccadic palsy is a selective gaze palsy affecting only leftward saccades but not leftward pursuit or vestibulo-ocular responses. A palsy affecting all types of eye movements should be designated as nonselective gaze palsy. In contrast, the terms “partial” or “complete” when applied to gaze palsy indicate whether some motion across midline in the paretic direction is present.
An even more fundamental distinction is between vertical and horizontal gaze palsies. The majority of gaze palsies affect 1 direction in 1 plane of eye movement only, reflecting the separation of the prenuclear control systems for vertical and horizontal eye movement.