Strabismus is a constant or periodic deviation of the visual axis of the eye from the fixation point, which leads to a violation of binocular vision. Disease is manifested by an external defect – a deviation of the eye/eye to nose or temple, up or down. In addition, a patient may have double vision, dizziness and headaches, decreased vision, amblyopia. Diagnostics includes ophthalmological examination (visual acuity check, biomicroscopy, perimetry, ophthalmoscopy, skiascopy, refractometry, biometric eye examination, etc.), neurological examination. Treatment is carried out with the help of glasses or contact correction, hardware procedures, pleoptic, orthoptic and diploptic techniques, surgical correction.
In pediatric ophthalmology, the disease (heterotropy or strabismus) occurs in 1.5-3% of children, with the same frequency in girls and boys. As a rule, disease develops at the age of 2-3, when the friendly work of both eyes is formed; however, a congenital form may also occur.
Disease is not only a cosmetic defect: this disease leads to disruption of almost all departments of the visual analyzer and can be accompanied by a number of visual disorders. With strabismus, the deviation of the position of one or both eyes from the central axis leads to the fact that the visual axes do not intersect on the fixed object. In this case, in the visual centers of the cerebral cortex, the monocular images perceived separately by the left and right eyes do not merge into a single visual image, but a double image of the object appears. To protect against double vision, the central nervous system suppresses the signals received from the squinting eye, which over time leads to amblyopia – a functional decrease in vision, in which the squinting eye is almost or not involved in the visual process at all. In the absence of treatment for strabismus, the development of amblyopia and vision loss occurs in about 50% of children.
In addition, the disease adversely affects the formation of the psyche, contributing to the development of isolation, negativism, irritability, as well as imposing restrictions on the choice of profession and sphere of human activity.
According to the timing of occurrence, there is a distinction between congenital (infantile – there is from birth or develops in the first 6 months) and acquired (usually develops up to 3 years). On the basis of the stability of the deviation of the eye, periodic (transient) and permanent are distinguished.
Taking into account the involvement of the eyes, disease can be unilateral (monolateral) and intermittent (alternating) – in the latter case, one or the other eye alternately squints.
According to the degree of severity, there are hidden (heterophoria), compensated (detected only during ophthalmological examination), subcompensated (occurs only when control is weakened) and decompensated (not controllable).
Depending on the direction in which the squinting eye deviates, horizontal, vertical and mixed strabismus are distinguished. Horizontal strabismus can be convergent (esotropia, converging) – in this case, the squinting eye is deflected to the bridge of the nose; and divergent (exotropia, diverging) – the squinting eye is deflected to the temple. In vertical form, there are also two forms with an upward displacement of the eye (hypertropia, supraverging strabismus) and downward (hypotropia, infraverging strabismus). In some cases, cyclotropy occurs – torsion heterotropy, in which the vertical meridian is tilted towards the temple (excyclotropy) or towards the nose (incyclotropy).
From the point of view of the causes of occurrence, friendly and paralytic non-friendly strabismus are distinguished. In 70-80% of cases, friendly strabismus is convergent, in 15-20% – divergent. Torsion and vertical deviations, as a rule, occur with paralytic strabismus.
With friendly strabismus, the movements of the eyeballs in various directions are preserved in full, there is no diplopia, there is a violation of binocular vision. Friendly strabismus can be accommodative, partially accommodative, non-accommodative.
Accommodative friendly strabismus develops more often at the age of 2.5-3 years due to the presence of high and medium degrees of farsightedness, myopia, astigmatism. In this case, the use of corrective glasses or contact lenses, as well as hardware treatment will help restore the symmetrical position of the eyes.
Signs of partially accommodative and non-accommodative strabismus appear in children of the 1st and 2nd year of life. With these forms of friendly strabismus, refractive error is far from the only cause of heterotropy, therefore surgical treatment is required to restore the position of the eyeballs.
The development of paralytic strabismus is associated with damage or paralysis of the oculomotor muscles due to pathological processes in the muscles themselves, nerves or brain. With paralytic strabismus, the mobility of the deflected eye towards the affected muscle is limited, diplopia and binocular vision impairment occur.
The occurrence of congenital (infantile) strabismus may be associated with a family history of heterotropy – the presence of strabismus in close relatives; genetic disorders (Crouzon syndrome, Down syndrome); teratogenic effect on the fetus of certain drugs, narcotic substances, alcohol; premature birth and the birth of a child with low body weight; cerebral palsy, hydrocephalus, congenital eye defects (congenital cataract).
The development of acquired strabismus can occur acutely or gradually. The causes of secondary friendly strabismus in children are ametropia (astigmatism, hyperopia, myopia); at the same time, divergent strabismus develops more often with myopia, and convergent strabismus with hypermetropia. Stress, high visual loads, childhood infections (measles, scarlet fever, diphtheria, flu) and general diseases (juvenile rheumatoid arthritis) occurring with high fever can provoke the development of strabismus.
At an older age, including in adults, acquired strabismus can develop against the background of cataracts, leukomas (cataracts), optic nerve atrophy, retinal detachment, macular degeneration, leading to a sharp decrease in vision of one or both eyes. Risk factors for paralytic strabismus include tumors (retinoblastoma), traumatic brain injuries, paralysis of the cranial nerves (oculomotor, block, diverting), neuroinfections (meningitis, encephalitis), strokes, fractures of the wall and bottom of the orbit, multiple sclerosis, myasthenia gravis.
An objective symptom of any kind of strabismus is the asymmetric position of the iris and pupil in relation to the eye slit.
With paralytic strabismus, the mobility of the deflected eye towards the paralyzed muscle is limited or absent. There is diplopia and dizziness, which disappear when one eye is closed, the inability to correctly assess the location of the object. With paralytic strabismus, the angle of the primary deviation (squinting eye) is less than the angle of the secondary deviation (healthy eye), i.e. when trying to fix the point with a squinting eye, the healthy eye deviates by a much larger angle.
A patient with paralytic strabismus is forced to turn or tilt his head to the side in order to compensate for visual impairment. This adaptive mechanism contributes to the passive transfer of the image of the object to the central fossa of the retina, thereby eliminating double vision and providing imperfect binocular vision. The forced tilt and turn of the head with paralytic strabismus should be distinguished from that with torticollis, otitis media.
In case of damage to the oculomotor nerve, ptosis of the eyelid, pupil dilation, deviation of the eye outward and downward, partial ophthalmoplegia and accommodation paralysis occur.
Unlike paralytic strabismus, with friendly heterotropy, diplopia is usually absent. The volume of movement of the squinting and fixing eye is approximately the same and unlimited, the angles of primary and secondary deviation are equal, the functions of the oculomotor muscles are not impaired. When fixing the gaze on an object, one or alternately both eyes deviate in any direction (to the temple, nose, up, down).
Friendly strabismus can be horizontal (converging or diverging), vertical (supraverging or infraverging), torsion (cyclotropy), combined; monolateral or alternating.
Monolateral strabismus leads to the fact that the visual function of the rejected eye is constantly suppressed by the central department of the visual analyzer, which is accompanied by a decrease in visual acuity of this eye and the development of dysbinocular amblyopia of varying degrees. With alternating strabismus, amblyopia, as a rule, does not develop or is expressed slightly.
In case of strabismus, a comprehensive ophthalmological examination is necessary with tests, biometric studies, examination of eye structures, refraction research.
When collecting anamnesis, the timing of the occurrence of strabismus and its connection with past injuries and diseases are clarified. During the external examination, attention is paid to the forced position of the head (with paralytic strabismus), the symmetry of the face and eye slits, the position of the eyeballs (enophthalmos, exophthalmos) are evaluated.
Then visual acuity is checked without correction and with trial lenses. Clinical refraction is studied to determine the optimal correction using skiascopy and computer refractometry. If strabismus disappears or decreases against the background of cycloplegia, this indicates the accommodative nature of the pathology. The anterior parts of the eye, transparent media and fundus are examined using biomicroscopy, ophthalmoscopy.
To study binocular vision, an eye-covering test is carried out: the squinting eye is deflected to the side; the fusion ability (the ability to merge images) is evaluated using the synoptophore apparatus. The angle of strabismus is measured (the magnitude of the deviation of the squinting eye), convergence is studied, and the volume of accommodation is determined.
If paralytic strabismus is detected, a neurologist’s consultation and additional neurological examination (electromyography, electroneurography, evoked potentials, EEG, etc.) are indicated.
With friendly strabismus, the main goal of treatment is to restore binocular vision, in which the asymmetry of the eye position is eliminated and visual functions are normalized. Measures may include optical correction, pleoptic-orthoptic treatment, surgical correction of strabismus, pre- and postoperative orthoptodiploptic treatment.
In the course of optical correction of strabismus, the aim is to restore visual acuity, as well as normalize the ratio of accommodation and convergence. For this purpose, glasses or contact lenses are taken. With accommodative strabismus, this is enough to eliminate heterotropy and restore binocular vision. Meanwhile, eyeglass or contact correction of ametropia is necessary for any form of strabismus.
Pleoptic treatment is indicated for amblyopia to increase the visual load on the squinting eye. For this purpose, occlusion (switching off from the process of vision) of the fixing eye can be prescribed, penalization can be used, hardware stimulation of the amblyopic eye can be prescribed (Amblyocore, Amblyopanorama, software-computer treatment, accommodation training, electrooculostimulation, laser stimulation, magnetostimulation, photostimulation, vacuum ophthalmic massage). The orthoptic stage treatment is aimed at restoring the coordinated binocular activity of both eyes. For this purpose, synoptic devices (Synoptophor), computer programs are used.
At the final stage treatment, diploptic treatment is carried out, aimed at developing binocular vision in natural conditions (training with Bagolini lenses, prisms); gymnastics is prescribed to improve eye mobility, training on a convergent trainer.
Surgical treatment can be undertaken if the effect of conservative therapy is absent for 1-1.5 years. Surgical correction of strabismus is optimal at the age of 3-5 years. In ophthalmology, surgical reduction or elimination of the angle of strabismus is often carried out in stages. To correct strabismus, two types of operations are used: weakening and strengthening the function of the oculomotor muscles. Weakening of muscle regulation is achieved by transplantation (recession) of a muscle or crossing of a tendon; strengthening of the action of the muscle is achieved by resection (shortening).
Before and after strabismus correction surgery, orthoptic and diploptic treatment is indicated to eliminate residual deviation. The success rate of surgical correction is 80-90%. Complications of surgical intervention may be hypercorrection and insufficient correction of strabismus; in rare cases – infections, bleeding, loss of vision.
The criteria for the treatment are the symmetry of the eye position, the stability of binocular vision, high visual acuity.
Prognosis and prevention
Strabismus treatment should be started as early as possible so that by the beginning of school the child is sufficiently rehabilitated with respect to visual functions. In almost all cases of strabismus, persistent, consistent and long-term complex treatment is required. Late and inadequate correction of strabismus can lead to irreversible vision loss.
Friendly accommodative strabismus is most successfully corrected; with late-diagnosed paralytic strabismus, the prognosis for restoring full visual function is unfavorable.
Prevention requires regular examinations of children by an ophthalmologist, timely optical correction of ametropia, compliance with the requirements of visual hygiene, dosage of visual loads. Early detection and treatment of any eye diseases, infections, prevention of skull injuries is necessary. During pregnancy, adverse effects on the fetus should be avoided.