Causes: paralysis of eye muscles, bulb rolls from affected muscle,
spasm of eye muscles, bulb rolls toward affected muscle, convergent
squint most common. Hold head still and move object in front of eyes,
imperfect movement toward paretic muscle or away from the spastic one.
Ptosis. Overfatigue. Debility. Nerve or brain lesion. Dislocation of
bulb. Treatment: treat any transient etiological factor, cerebral
congestion, parasitisms, debility, anæmia. Tenotomy of rectus: advance
of paretic rectus.
Strabismus may be due to a variety of causes, among others to the
following:
=Paralysis= of one of the ocular muscles. When the eyes are turned in
the direction away from the affected muscle the muscle is deficient in
power. It may be the external rectus (abducent nerve) producing
convergent squint. It may be of the superior oblique muscle (4th or
pathetic nerve) causing a faulty movement of the eye downward and inward
or a slightly convergent squint. Divergent squint commonly indicates
paralysis of upper, lower and inner recti, and the inferior oblique (3d
or oculo motor nerve): this is usually associated with ptosis or
drooping of the upper lid, the levator of which is supplied by the same
nerve. The existence of squint is usually so marked that no special
method of examination is required. If otherwise, however, the animal’s
head may be held still and some object which will attract his attention
is moved before the eyes, outward and inward, when the affected eye
moving in the direction of the paralytic muscle will lag visibly behind
its fellow. These conditions are usually due to lesions in the
respective nerves or their cerebral ganglia.
=Spasmodic or Spastic Squint= is the exact antithesis of the above, the
eye turning toward the muscle which is the seat of spasm. It may be seen
in certain cases of rabies and is always due to disorder of the central
nervous ganglia.
In some cases squinting is associated with over-fatigue, or debility,
and then usually partakes of the paralytic character.
In the lower animals convergent strabismus has been most frequently
observed. Brouwer records a case in the horse and Koch a congenital one
in the cow. Zschokke reports a case in the cow connected with an angioma
at the base of the brain. Other forms are noted by Peters, Barrier,
Bayer and others. Stockfleth quotes a case in the dog following
prolapsus bulbi and doubtless connected with injury to ocular muscles or
nerves, sustained in the accident.
_Treatment_ will vary with the ascertained cause. As a rule cases that
depend on structural changes in the brain are hopeless. Those that
depend on temporary congestion or other transient disorder of that organ
may recover when that has been overcome. In cases in which debility is a
prominent feature, tonics, moderate exercise in the open air and general
hygienic care are demanded. The final resort in bad cases is tenotomy of
the rectus on the side toward which the eye turns. In man when this is
found to be insufficient the opposing weak or paretic muscle is also
advanced. The tendon close to its sclerotic attachment is laid bare by
incision, and a silk or catgut thread is passed through each border,
upper and lower. The tendon is now cut through with scissors on the
corneal side of the sutures and, by means of their needles, the latter
are passed through the conjunctiva and capsule of Tenon, from within
outward and close to the margin of the cornea. The sutures are now tied
somewhat tighter than is absolutely necessary to properly balance the
eye so as to allow some room for relaxation in healing. We are not aware
that this measure of advancement has been employed in the domestic
animals.