Paralytic strabismus is a disease characterized by a deviation of the visual axis of the eye from the general fixation point. Clinical manifestations of the disease are impaired mobility of the eyeball, double vision, headache, increased visual fatigue. In the process of diagnosing paralytic strabismus, the degree of deviation and mobility of the eyeballs is studied, the fields of vision and torticollis are examined, electromyography is performed. Treatment is carried out conservatively (special gymnastics, occlusive dressing, electrophoresis with muscle relaxants) or surgically.
Paralytic strabismus (paretic strabismus, heterotropia) is a widespread pathology. The disease occurs in all age groups. According to statistics, paretic strabismus is diagnosed in children 2-3 times more often than in adults. During the newborn period, signs of strabismus are detected in 2% of infants. In 70% of cases, in the absence of timely treatment, complications develop, the most frequent of which is dysbinocular amblyopia. Male and female individuals suffer with the same frequency. The disease is widespread everywhere.
The disease is based on paralysis or paresis of one or more oculomotor muscles. In the etiology of congenital strabismus, the leading role is assigned to birth trauma, abnormalities of the structure of the visual and nervous systems, intrauterine damage to the organ of vision in toxoplasmosis, rubella, measles. The main causes of the acquired variant of pathology are:
- Damage to the oculomotor muscles. Violation of the integrity of the eye muscles is one of the complications of traumatic brain injury, contusion of the eye or other damage to the organ of vision. Possible iatrogenic deviation of the eyeball from the fixation point after surgery.
- Infectious diseases. Brain and eye infections can be triggers. Strabismus is a frequent manifestation of neurosyphilis, leptomeningitis, and neurotuberculosis. The lesion of the eye muscles in trichinosis is also accompanied by a strabismus clinic.
- Malignant neoplasms. Compression of the eyeball by a tumor leads to a restriction of its mobility and the development of an orbital form of the disease. When cranial nuclei and stem structures are involved in the oncological process, a central form of pathology is observed.
- Myositis. Inflammation of one or more oculomotor muscles is a transient phenomenon during intoxication. At the same time, dermatomyositis, polymyositis, and polyfibromyositis are often irreversible.
- Neuritis. The most common symptoms of the disease are associated with toxic infectious neuritis. Inflammation of the nerves responsible for the innervation of the oculomotor muscles occurs due to hypothermia, against the background of viral or bacterial diseases.
- Damage to the eye socket. Pathological changes in the bone walls of the orbit with periostitis or subperiosteal abscess lead to compression of the eyeball and provoke a clinical picture of strabismus.
With paralytic strabismus, there is a lesion of the nuclei of the oculomotor, block or diverting nerves. An important role in the pathogenesis is assigned to the pathology of the base of the brain or eye socket. Less often, the development of the disease is caused by direct damage to the nerve fibers innervating the corresponding oculomotor muscles. In case of injury or neuritis, the passage of an impulse along a nerve fiber is disrupted. Strabismus may be accompanied by external or internal ophthalmoplegia. With the external form of the disease, the external muscles of the eye are paralyzed, but the pupil sphincter and the ciliary muscle function normally. With internal ophthalmoplegia, only the pupillary sphincter and the ciliary muscle are affected.
There are congenital and acquired variants of the disease. Isolated lesion of one muscle, involvement of two or more oculomotor muscles is possible. The process can be one- or two-sided. In accordance with the pathogenetic classification , the following forms of paralytic strabismus are distinguished:
- Nuclear. The development of this type of disease is associated with direct damage to the cranial nuclei in diseases of the brain (encephalitis, neurosyphilis, multiple sclerosis). Detection of degenerative-dystrophic changes at the nuclear level is an unfavorable prognostic criterion.
- Stem. In this variant of pathology, the damage is localized at the level of the base of the brain, therefore strabismus is often called basal. The toxic, angiogenic, infectious and traumatic nature of the disease has been proven.
- Orbital. This is the most favorable form of Strabismus. The etiological factor is the lesion of the orbit (periostitis, subperiosteal abscess). After the elimination of the provoking process, the functions of the visual organ are restored in full.
The mobility of the eye on the affected side is limited or impossible. The movements of the eyeball are sharply hindered. The patient cannot direct his gaze in the direction opposite from the damaged muscle. When focusing the diseased eye on a certain object, the healthy one deviates to the side. Persons with acquired form complain of double vision before the eyes, frequent dizziness. With the congenital variant, diplopia does not occur, the clinical picture of the disease often resembles the symptoms of friendly strabismus. Performing visual work leads to rapid fatigue.
To reduce the severity of symptoms, the patient closes the “squinting” eye or forcibly turns his head towards the lesion. The omission of the upper eyelid indicates the paralysis of the oculomotor nerve. The eyeball is deflected outwards and downwards, and movements are possible only in the specified directions. Because of the accommodation spasm, there is no reaction of the pupil to light. With multiple lesions (involvement of three nerves in the pathological process), the eye is absolutely motionless. When viewing an object with a sick eye, the patient is not able to accurately indicate its location.
Paralytic strabismus is most often complicated by dysbinocular amblyopia, which is due to the limited participation of one of the eyeballs in the act of vision. At the same time, there is a progressive decrease in visual acuity. Due to the formation of new reflex connections, abnormal retinal correspondence is formed in patients with a congenital variant of the disease. The long course of the disease contributes to the occurrence of scotoma inhibition, which is a compensatory mechanism. There is an increased risk of refractive errors (myopia, less often hypermetropia).
To make a diagnosis, it is necessary to determine which of the oculomotor muscles is involved in the pathological process. During a physical examination, the doctor pays attention to the mobility of the eyeballs, the width of the pupillary opening and the condition of the anterior segment of the eye. All patients undergo visometry to assess visual acuity. Specific diagnostics is based on:
- Studying the degree of deviation. At different positions of the direction of view, the size of the angle of strabismus is measured. In the presence of the disease, the deviation angle increases as the gaze moves towards the affected muscle. Additionally, the magnitude of the deviation of the eyeball is determined by the Hirschberg method.
- The study of eye mobility. The doctor moves a special object of fixation (the tip of a pen, pencil) up, down, right and left, notes in which direction the deviation of the eye is impossible. Then the ophthalmologist with the help of special tables clarifies the lesion of which muscle the data obtained correspond to.
- The study of torticollis. The forced position of the patient’s head depends on which muscle is paralyzed, which can be used for diagnosis. There are three possible options: the first – the head is raised or lowered, the second – the head is tilted to the shoulder, the third – the face is turned to the right or left.
- Determining the field of view. The Hess method of co-ordimetry is used. The research technique involves the relative separation of the visual fields using a green and red filter. With the help of nine fixation points on the coordinate scheme, the zone of “action” of the paralyzed muscle is marked.
- Electromyography. This technique allows us to study the bioelectric activity of muscles. The results of the study make it possible to judge the functional activity of the nerve responsible for muscle innervation. First, surface, then local electromyography is performed.
Differential diagnosis is carried out between paresis and paralysis of the oculomotor muscles. With paresis, the limitation of the mobility of the eye, as well as its deviation to the side, are less pronounced. Visually, the deviation is practically not determined. For a complete neurological examination, a consultation with a neurologist is indicated.
With the acquired form of strabismus, the treatment of the underlying disease is carried out (removal of pathological neoplasms, therapy of infectious diseases). Often this is enough to level deviation and diplopia. The aim of symptomatic treatment is to restore the symmetrical position of the eyes, eliminate secondary manifestations of the disease. With a mild course, conservative therapy is reduced to performing visual gymnastics and orthoptic exercises to merge double images. To minimize the severity of diplopia, glasses with prismatic lenses are used. Temporary occlusion of the affected eye is effective. Physiotherapy treatment includes the use of electrophoresis with muscle relaxants, electrical stimulation of the oculomotor muscles and reflexotherapy.
Surgical intervention is advisable only for persistent paralysis or paresis. The operation is performed after 6-12 months of treatment in the absence of progression of the process. In the congenital form of strabismus, surgical intervention is recommended after reaching 3-4 years. Surgical treatment consists in plastic surgery of the oculomotor muscles. Minimal eye mobility is restored immediately after surgery. For full compensation in the postoperative period from 2-4 days, special gymnastics is performed to develop oculomotor muscles.
Prognosis and prevention
The prognosis for paretic strabismus is more often favorable. It is easier to achieve a symmetrical eye position than to ensure the restoration of binocular vision. Specific preventive measures have not been developed. Non-specific prevention is reduced to the prevention of industrial and household injuries. In the event of infectious diseases with a high tropicity to the organ of vision, it is necessary to consult an ophthalmologist for preventive purposes. To reduce the risk of developing a congenital form of paralytic strabismus, it is recommended to perform a cesarean section with a large fetus, a mismatch in the size of the fetus and the pelvis of a pregnant woman.