STRABISMUS. SQUINTING. LACK OF MUSCULAR BALANCE.
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.
NYSTAGMUS. OSCILLATORY MOVEMENT OF THE EYE.
This consists in spasmodic involuntary oscillation of the eyeball in a horizontal, lateral, oblique or rotary direction. In animals it has been seen in connection with poisoning and brain diseases. Johné has observed it in horses in cerebro-spinal meningitis, Wenderhold in epilepsy, and Möller in chloroform anæsthesia. Möller has further seen it in puppies with congenital microphthalmos, and Siedamgrotzky in swine which had been poisoned by herring brine.