Correspondence - ICO Library

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Binocular Vision & Inferior Oblique Muscle Palsy with ‘Paradoxical’ V-Pattern Strabismus FIRST Quarter of 2011
Strabology Quarterly© E. Khawam, MD and D. Fahed, MD Volume 26 (No.1)
A Medical Scientific e-Periodical Pages 51-60
INTRODUCTION
In patients with cyclovertical muscle
palsy, secondary A- or V-pattern to the
horizontal deviation develops along with the
vertical and torsional deviations (1).
The pathologic physiology that
produces a secondary horizontal deviation in
all isolated cyclovertical muscle pareses
occurs when the paretic muscle develops a
weakness of its horizontal component while,
according to Herring’s and Sherington’s laws,
the antagonist and yoke muscles of the paretic
muscle develop overactions of their horizontal
components (2).
The most commonly encountered
secondary muscle anomalies in cyclovertical
muscle palsies are 1) overaction of the direct
antagonist muscle and overaction of its yoke
muscle in the fellow eye, and 2) underaction
of the yoke of the antagonist, described by
Chavasse as “Inhibitional palsy of the
contralateral antagonist” (3).
A mnemonic rule (4) to identify the
muscle involved in an inhibitional palsy in all
isolated cyclovertical muscle palsies would be
to change oblique to rectus –or rectus to
oblique, the right eye to left eye –or vice
versa, and keep superior or inferior
unchanged.
Less well known and less encountered
secondary muscle anomalies in cyclovertical
muscle palsies are described by Urist (5), and
called the “Synergistic Hyper” and
“Synergistic Hypo”. Urist points out the
presence of two “synergistic hyper”:
overaction of the synergist of the antagonist,
and overaction of the synergist of the yoke.
He also describes two “synergistic hypo”:
underaction of the synergist of the paretic
muscle, and underaction of the synergist of
the yoke of the antagonist. So, when
underaction of the depressors is produced in
one eye, there will tend to be underaction of
the elevators in the opposite eye, or vice
versa; and conversely, when overaction of the
depressors occurs in one eye, there will be
overaction of the elevators in the opposite eye,
and vice versa.
Starting with a known paretic vertical
muscle (5), by constructing the diagram
shown in Figure 1, below all of the possible
secondary vertical deviations can be easily
determined. To explain this, the steps of
constructing the diagram are described by
Urist (5) as follows: represent underaction of
the muscles by a solid triangle, and overaction
of the muscles by arrows pointing in the
direction of the overaction. Place the base of
the triangle in the field of action of the paretic
muscle of the involved eye; reverse this
triangle in the contralateral eye.
Taking a right superior oblique (SO)
palsy as an example, there will be underaction
of the right eye looking down, so the triangle
is placed with its base down for this eye. For
the left eye, the base is reversed. Next, all the
muscles are marked in relation to their field of
action.
Figure 1 (Khawam & Fahed): Adapted from
Urist: Secondary deviations in right superior
oblique muscle palsy.