The term
“gaze palsy” is best restricted to 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.
A fundamental distinction is
between vertical and horizontal gaze palsies. Most
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.
Reduction of eye movements in
all planes is best termed “generalized
ophthalmoparesis.” These reductions are most
commonly myopathic, occurring with
mitochondrial disorders
(chronic
progressive external
ophthalmoplegia,
Kearns-Sayre syndrome,
MELAS)
or muscular dystrophies (myotonic
dystrophy,
oculopharyngeal dystrophy, 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
response. A palsy affecting all types of eye
movements should be designated as a nonselective
gaze palsy. Most vertical gaze palsies are selective
in nature.
In contrast, the terms “partial”
or “complete” when applied to gaze palsy indicate
whether some motion across midline in the paretic
direction is present.
vertical gaze palsy is usually induced by midbrain
lesions. Lesions commonly covered the rostral
midbrain, including the rostral interstitial
nucleus, dorsomedial to the red nucleus. Vertical
vestibulo-ocular response frequently appears normal
, but is sometimes absent . Torsional and vertical
nystagmus may
occur if the interstitial nucleus of Cajal is
involved . Bell phenomenon can be absent .
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