Nystagmus is a pathology characterized by involuntary oscillatory eye movements. Clinical symptoms include rapid fluctuations of the eyeballs in the vertical, horizontal, less often – oblique or circular direction. The accommodative ability is impaired, which is manifested by visual dysfunction. Objective examination, microperimetry, electronystagmography, visometry, refractometry, computed tomography of the brain are used for diagnosis. Conservative therapy is based on the use of anticonvulsants and antiepileptic drugs. Less often, surgical correction of the eyeball position is indicated.
Nystagmus is a widespread nosology in practical ophthalmology. According to statistics, among visually impaired children, the congenital form of pathology is diagnosed in 20-40% of patients. It is often possible to establish the etiology of involuntary oscillatory movements of the eye. The idiopathic type occurs with a frequency of 1:3000. Horizontal nystagmus is the most common, while oblique and rotational variants are extremely rare. In the general structure of the lesion of the visual organ, the horizontal type occupies 18%. There are no geographical features of epidemiology.
Causes of nystagmus
Congenital nystagmus occurs against the background of neurological disorders. The hereditary nature of the disease is evidenced by the appearance of clinical symptoms against the background of Leber’s congenital amaurosis or albinism. The main reasons for the development of the acquired form:
- Pathology of the brain. Nystagmus in adulthood can be one of the symptoms of multiple sclerosis or malignant neoplasm. The sudden appearance of symptoms may indicate a stroke.
- Traumatic brain injury. Involuntary eye fluctuations are associated with damage to the optic nerves or the occipital lobe of the cerebral cortex.
- Intoxication. The disease occurs due to the toxic effects of alcoholic beverages, an overdose of anticonvulsants and sleeping pills.
- Lesion of the vestibular apparatus. Clinical manifestations are preceded by damage to the central or peripheral parts of the vestibular analyzer. Often, the development of the acquired form provokes the defeat of the semicircular canals of the inner ear.
- Decreased visual acuity. Nystagmus can develop due to a marked decrease in visual acuity in patients with mature cataracts, a history of traumatic damage to the visual organ, or with complete blindness (amaurosis).
Spontaneous movements of the eyeballs are based on decompensation of the tone of the membranous part of the labyrinth of the inner ear. Normally, nerve impulses are generated simultaneously from both sides and transmitted at the same speed, which allows the eyes to be at rest or to carry out friendly movements. Increasing the tone in the maze from a certain side leads to the development of nystagmus.
When the peripheral and central parts of the vestibular analyzer are affected, the occurrence or change in the severity of clinical manifestations is noted with a change in position. This is due to the secondary involvement of semicircular tubules in the pathological process. The molecular mechanism of the development of congenital idiopathic nystagmus has not been fully studied. Scientists believe that it is based on a mutation of the FRMD7 gene, which is inherited by the X-linked type. However, cases of autosomal dominant and autosomal recessive inheritance have also been observed in clinical practice.
Depending on the time of the appearance of the first symptoms, congenital and acquired nystagmus are distinguished. The innate form includes latent and manifest-latent types. The acquired variant is classified according to etiology into neurogenic and vestibular. From a clinical point of view , there are:
- Pendulum-like (undulating). It is characterized by the same magnitude and speed of the phases of oscillations of the eyeballs.
- Push-like. It is distinguished by rhythmic eye movements, in which the eyeball is directed slowly in one direction, and quickly in the other. If in the fast phase the eyes are directed to the left, then we are talking about a left-sided form, movements to the right indicate a right-sided variant.
- Mixed. This variant of the disease combines push-like and undulating forms.
- Associated. The eyeballs move together with the same amplitude in a pendulum-like or push-like type.
- Dissociated. The nature of the movements of one eye does not coincide in direction and amplitude with the other eyeball.
Symptoms of nystagmus
In most cases, the first manifestations of the disease occur in early childhood or from the moment of birth. The symptoms of the acquired form develop immediately after the action of the etiological factor. Patients complain of repetitive oscillatory eye movements. The direction of oscillation can be horizontal, vertical, less often oblique or circular. The patient is unable to focus on the subject under consideration. The ability to adapt to changes in external conditions is impaired. The decrease in visual functions is caused not by a pathology of clinical refraction, but by a reduced accommodation reserve.
The patient cannot completely stop the manifestations of nystagmus, but the magnitude of the oscillations decreases somewhat when the direction of gaze changes, the position of the head or the maximum focus of attention on a certain object. To reduce the severity of clinical symptoms, the patient assumes a forced position with the lowest frequency of movements. Head turns to the side or torticollis (tilt) are common. The choice of position is determined by the zone of relative rest, in which the amplitude of movements decreases and the accommodative ability improves.
Symptoms are most noticeable in stressful conditions, with excitement or fatigue. The duration of the manifestations is influenced by the nature of the movements. With the pendulum type, the duration of nystagmus is longer than with the jolt-like variant of the disease. The properties of oscillatory movements may vary. The change of manifestations provokes the appearance of an object in the field of view, a change in its size or brightness. A certain role is assigned to the factor of visual concentration and even mood. The form of the disease is determined by eye movements that dominate the clinical picture.
A common complication of nystagmus is secondary alternating convergent strabismus, which often develops in patients with a dissociated form. The characteristics of strabismus are determined by the course of the underlying disease. The pathology is accompanied by reversible visual dysfunction – amblyopia and mixed astigmatism. The acquired variant is complicated by a number of vestibular disorders (dizziness, impaired coordination, headache). Due to the need to often keep the head in a forced position, the development of compensatory torticollis is possible. Individuals with a history of vestibular nystagmus are prone to recurrent labyrinthitis.
To make a diagnosis, an objective examination of the patient is sufficient. During external examination, it is possible to visualize involuntary eye movements. To determine the direction of the nystagmus, the patient is asked to focus his eyes on a pen or a special pointer. The ophthalmologist swipes the instrument up, down, right and left. The shape of the lesion is determined in the direction of the fast component. To study the etiology of the disease and the choice of further management tactics is used:
- Microperimetry. The technique allows you to determine the fixation point on the inner shell of the eyeball, register the parameters of the optical nystagmus and study the sensitivity of the retina. The method makes it possible to monitor the condition of patients to assess the effectiveness of therapeutic measures.
- Electronistagmography (ENG). The study is based on the registration of biopotentials that arise between the cornea and the retina. In persons with involuntary eye movements, the electric axis shifts, which is accompanied by an increase in the difference of the corneoretinal biopotential to 100-300 mv.
- Visometry. Patients have a decrease in visual acuity due to functional disorders of the visual analyzer.
- Refractometry. Diagnosis is carried out in order to establish the type of clinical refraction. Patients with nystagmus often have a violation of the ability to accommodate, myopia. Hypermetropia is rarely diagnosed.
- CT scan of the brain. Computed tomography is used to detect pathological neoplasms or signs of dislocation of brain structures, which may underlie the occurrence of pathology.
Treatment of nystagmus
Therapeutic tactics depend on the severity of symptoms and the form of nystagmus. Etiotropic therapy is determined by the underlying disease. To eliminate nystagmus , it is used:
- Conservative therapy. It is used if clinical manifestations develop against the background of central vestibulopathy. The use of neurotropic drugs from the group of anticonvulsant, antiepileptic drugs is recommended.
- Surgical intervention. The purpose of surgical treatment is to form a position of relative rest of the eyes by restoring the physiological position. To do this, the structural features of the oculomotor muscles are changed.
Symptomatic treatment is based on eyeglass or contact correction of visual acuity. The use of contact lenses is recommended, since when the eye moves, the lens center shifts with it, visual dysfunction does not develop. In some cases, botox injections are carried out into the orbital cavity to limit small-scale eye movements.
Prognosis and prevention
The prognosis for life and visual functions in nystagmus is favorable. Correct therapy of the underlying disease allows you to completely eliminate the clinical manifestations of pathology. Specific prevention has not been developed. Non-specific preventive measures are reduced to timely diagnosis and treatment of lesions of the brain, vestibular apparatus and visual organ. If involuntary movements of the eyeballs are detected in patients taking anticonvulsants or hypnotics, it is necessary to adjust the dosage of medicines.